diff --git a/resources/js/components/charts/treemap-chart.tsx b/resources/js/components/charts/treemap-chart.tsx
index 011bad8b..a519eb4e 100644
--- a/resources/js/components/charts/treemap-chart.tsx
+++ b/resources/js/components/charts/treemap-chart.tsx
@@ -1,6 +1,6 @@
 import { index as transactionsIndex } from '@/actions/App/Http/Controllers/TransactionController';
 import { usePrivacyMode } from '@/contexts/privacy-mode-context';
-import { SankeyCategory } from '@/hooks/use-cashflow-data';
+import { SankeyCategory, SankeyData } from '@/hooks/use-cashflow-data';
 import { useChartColors } from '@/hooks/use-chart-color-scheme';
 import { useLocale } from '@/hooks/use-locale';
 import { cn } from '@/lib/utils';
@@ -8,8 +8,8 @@ import { formatCurrency } from '@/utils/currency';
 import { __ } from '@/utils/i18n';
 import { router } from '@inertiajs/react';
 import { format } from 'date-fns';
-import { useMemo } from 'react';
-import { ResponsiveContainer, Treemap } from 'recharts';
+import { useEffect, useMemo, useState } from 'react';
+import { ResponsiveContainer, Tooltip, Treemap } from 'recharts';
 
 interface TreemapChartProps {
     categories: SankeyCategory[];
@@ -26,6 +26,7 @@ interface TreemapDatum {
     size: number;
     color: string;
     categoryId: string;
+    children?: TreemapDatum[];
     // Satisfies recharts' TreemapDataType index signature.
     [key: string]: unknown;
 }
@@ -72,24 +73,22 @@ function CategoryNode({
     size = 0,
     color = 'var(--color-chart-4)',
     categoryId,
+    children,
     currency,
     locale,
     isPrivacyModeEnabled,
 }: TreemapNodeProps) {
-    // depth 0 is the invisible root; only leaves carry a category.
+    // depth 0 is the invisible root; only leaves/parents carry a category.
     if (depth < 1 || !categoryId) {
         return null;
     }
 
     const showName = width >= 40 && height >= 22;
     const showAmount = width >= 55 && height >= 40;
+    const hasChildren = Array.isArray(children) && children.length > 0;
 
     return (
         <g style={{ cursor: 'pointer' }}>
-            <title>
-                {name}:{' '}
-                {maskIfPrivate(size, currency, locale, isPrivacyModeEnabled)}
-            </title>
             <rect
                 x={x}
                 y={y}
@@ -107,7 +106,7 @@ function CategoryNode({
                     y={y + 18}
                     className="fill-white text-[12px] font-medium"
                 >
-                    {truncate(name, width)}
+                    {truncate(hasChildren ? `${name} ›` : name, width)}
                 </text>
             )}
             {showAmount && (
@@ -128,6 +127,42 @@ function CategoryNode({
     );
 }
 
+interface TreemapTooltipProps {
+    active?: boolean;
+    payload?: Array<{ payload?: TreemapDatum }>;
+    currency: string;
+    locale: string;
+    isPrivacyModeEnabled: boolean;
+}
+
+function TreemapTooltip({
+    active,
+    payload,
+    currency,
+    locale,
+    isPrivacyModeEnabled,
+}: TreemapTooltipProps) {
+    const node = payload?.[0]?.payload;
+
+    if (!active || !node?.name) {
+        return null;
+    }
+
+    return (
+        <div className="rounded-lg border border-border/50 bg-background px-3 py-2 text-xs shadow-xl">
+            <div className="font-medium">{node.name}</div>
+            <div className="text-muted-foreground tabular-nums">
+                {maskIfPrivate(
+                    node.size,
+                    currency,
+                    locale,
+                    isPrivacyModeEnabled,
+                )}
+            </div>
+        </div>
+    );
+}
+
 export function TreemapChart({
     categories,
     total,
@@ -141,17 +176,101 @@ export function TreemapChart({
     const { isPrivacyModeEnabled } = usePrivacyMode();
     const { categoryBarColor } = useChartColors();
 
+    // Nest mode needs the full tree upfront, so prefetch each parent's children.
+    // ponytail: one level deep — matches the old sankey; deeper nesting would
+    // need recursive fetching and rollUp already caps categories at depth 3.
+    const [childrenByParent, setChildrenByParent] = useState<
+        Record<string, SankeyCategory[]>
+    >({});
+
+    const periodKey = period
+        ? `${period.from.getTime()}-${period.to.getTime()}`
+        : '';
+
+    useEffect(() => {
+        if (!period) {
+            return;
+        }
+
+        const parents = categories.filter(
+            (item) => item.has_children && item.category_id,
+        );
+
+        if (parents.length === 0) {
+            setChildrenByParent({});
+            return;
+        }
+
+        const from = format(period.from, 'yyyy-MM-dd');
+        const to = format(period.to, 'yyyy-MM-dd');
+        let cancelled = false;
+
+        Promise.all(
+            parents.map(async (parent) => {
+                const response = await fetch(
+                    `/api/cashflow/sankey?from=${from}&to=${to}&parent=${parent.category_id}`,
+                );
+                const json: SankeyData = await response.json();
+                const kids =
+                    mode === 'income'
+                        ? json.income_categories
+                        : json.expense_categories;
+
+                return [parent.category_id, kids] as const;
+            }),
+        )
+            .then((entries) => {
+                if (cancelled) {
+                    return;
+                }
+
+                const next: Record<string, SankeyCategory[]> = {};
+                entries.forEach(([id, kids]) => {
+                    next[id] = kids;
+                });
+                setChildrenByParent(next);
+            })
+            .catch((error) => {
+                console.error('Failed to fetch subcategories:', error);
+            });
+
+        return () => {
+            cancelled = true;
+        };
+        // categoryBarColor is intentionally excluded: it changes identity every
+        // render and colours are applied in the memo below, not here.
+        // eslint-disable-next-line react-hooks/exhaustive-deps
+    }, [categories, periodKey, mode]);
+
     const data = useMemo<TreemapDatum[]>(() => {
-        return [...categories]
-            .filter((item) => item.amount > 0)
-            .sort((a, b) => b.amount - a.amount)
-            .map((item, index) => ({
-                name: item.category.name,
-                size: item.amount,
-                color: categoryBarColor(item.category.color, index),
-                categoryId: item.category.id,
-            }));
-    }, [categories, categoryBarColor]);
+        const toDatum = (
+            item: SankeyCategory,
+            index: number,
+        ): TreemapDatum => ({
+            name: item.category.name,
+            size: item.amount,
+            color: categoryBarColor(item.category.color, index),
+            categoryId: item.category_id ?? '',
+        });
+
+        const sortPositive = (items: SankeyCategory[]): SankeyCategory[] =>
+            [...items]
+                .filter((item) => item.amount > 0)
+                .sort((a, b) => b.amount - a.amount);
+
+        return sortPositive(categories).map((item, index) => {
+            const datum = toDatum(item, index);
+            const kids = item.category_id
+                ? childrenByParent[item.category_id]
+                : undefined;
+
+            if (kids && kids.length > 0) {
+                datum.children = sortPositive(kids).map(toDatum);
+            }
+
+            return datum;
+        });
+    }, [categories, childrenByParent, categoryBarColor]);
 
     if (total === 0 || data.length === 0) {
         return (
@@ -168,7 +287,7 @@ export function TreemapChart({
     }
 
     const navigate = (categoryId: unknown) => {
-        if (typeof categoryId !== 'string' || !period) {
+        if (!categoryId || typeof categoryId !== 'string' || !period) {
             return;
         }
 
@@ -184,15 +303,31 @@ export function TreemapChart({
     };
 
     return (
-        <div className={cn('w-full', className)}>
+        <div
+            className={cn(
+                'w-full',
+                // Recharts renders the nest breadcrumb with hardcoded inline
+                // styles; override them to match the design system.
+                '[&_.recharts-treemap-nest-index-box]:!mr-1 [&_.recharts-treemap-nest-index-box]:!rounded [&_.recharts-treemap-nest-index-box]:!bg-muted [&_.recharts-treemap-nest-index-box]:!px-2 [&_.recharts-treemap-nest-index-box]:!text-foreground',
+                className,
+            )}
+        >
             <ResponsiveContainer width="100%" height={height}>
                 <Treemap
                     data={data}
                     dataKey="size"
+                    type="nest"
+                    nodeGap={2}
                     // ponytail: key by mode so a toggle switch re-lays out cleanly
                     key={mode}
                     isAnimationActive={false}
-                    onClick={(node) => navigate(node.categoryId)}
+                    // In nest mode onClick fires on every node; parents zoom in,
+                    // so only leaves navigate to their transactions.
+                    onClick={(node) => {
+                        if (!node.children) {
+                            navigate(node.categoryId);
+                        }
+                    }}
                     content={
                         <CategoryNode
                             currency={currency}
@@ -200,7 +335,17 @@ export function TreemapChart({
                             isPrivacyModeEnabled={isPrivacyModeEnabled}
                         />
                     }
-                />
+                >
+                    <Tooltip
+                        content={
+                            <TreemapTooltip
+                                currency={currency}
+                                locale={locale}
+                                isPrivacyModeEnabled={isPrivacyModeEnabled}
+                            />
+                        }
+                    />
+                </Treemap>
             </ResponsiveContainer>
         </div>
     );