diff --git a/webui/package.json b/webui/package.json
index 3206ec5..32fc4e1 100644
--- a/webui/package.json
+++ b/webui/package.json
@@ -6,6 +6,9 @@
   "main": "src/index.ts",
   "module": "src/index.ts",
   "types": "src/index.ts",
+  "scripts": {
+    "test:organizations-tree": "node scripts/test-organizations-tree-structure.mjs"
+  },
   "exports": {
     ".": {
       "types": "./src/index.ts",
diff --git a/webui/scripts/test-organizations-tree-structure.mjs b/webui/scripts/test-organizations-tree-structure.mjs
new file mode 100644
index 0000000..9d2ada4
--- /dev/null
+++ b/webui/scripts/test-organizations-tree-structure.mjs
@@ -0,0 +1,24 @@
+import { readFileSync } from "node:fs";
+
+function assert(condition, message) {
+  if (!condition) throw new Error(message);
+}
+
+const source = readFileSync(
+  new URL("../src/features/organizations/OrganizationsPage.tsx", import.meta.url),
+  "utf8"
+);
+const styles = readFileSync(
+  new URL("../src/styles/organizations.css", import.meta.url),
+  "utf8"
+);
+
+assert(source.includes("ExplorerTree,"), "Organizations imports the central ExplorerTree");
+assert(source.includes("<ExplorerTree"), "the organization hierarchy uses ExplorerTree");
+assert(source.includes("collapsible={false}"), "the always-expanded hierarchy uses the non-collapsible contract");
+assert(source.includes("renderNodeActions="), "per-unit controls use the sibling node-action slot");
+assert(source.includes("<IconButton"), "per-unit controls use the central icon-only action primitive");
+assert(!source.includes("renderUnitTreeNodes"), "the custom recursive renderer was removed");
+assert(!source.includes("organizations-tree-row"), "the custom tree row was removed");
+assert(!source.includes("organizations-tree-node"), "the custom tree node was removed");
+assert(!styles.includes("organizations-tree-"), "Organizations no longer owns shared tree styling");
diff --git a/webui/src/features/organizations/OrganizationsPage.tsx b/webui/src/features/organizations/OrganizationsPage.tsx
index c7923cc..3184a71 100644
--- a/webui/src/features/organizations/OrganizationsPage.tsx
+++ b/webui/src/features/organizations/OrganizationsPage.tsx
@@ -8,7 +8,9 @@ import {
   DataGrid,
   Dialog,
   DismissibleAlert,
+  ExplorerTree,
   FormField,
+  IconButton,
   LoadingFrame,
   ModuleSubnav,
   PageTitle,
@@ -1000,41 +1002,42 @@ export default function OrganizationsPage({
     );
   }
 
-  function renderUnitTreeNodes(parentId = "", depth = 0, seen: ReadonlySet<string> = new Set()): JSX.Element[] {
-    return (unitsByParentId.get(parentId) ?? []).flatMap((unit) => {
-      if (seen.has(unit.id)) return [];
-      const nextSeen = new Set(seen);
-      nextSeen.add(unit.id);
-      return [
-      <div className="organizations-tree-row" key={unit.id}>
-        <button
-          type="button"
-          className={`organizations-tree-node ${selectedUnitId === unit.id ? "active" : ""}`.trim()}
-          style={{ paddingLeft: `${10 + depth * 18}px` }}
-          onClick={() => setSelectedUnitId(unit.id)}
-        >
-          <strong>{unit.name}</strong>
-          <span>{unitTypeById.get(unit.unit_type_id || "")?.name ?? "i18n:govoplan-organizations.no_unit_type.73e799f5"}</span>
-        </button>
-        <Button type="button" variant="ghost" disabled={!canWriteUnits || busy} onClick={() => addSubunit(unit)} title="i18n:govoplan-organizations.add_subunit.8256a8f7">
-          <Plus size={16} aria-hidden="true" /> i18n:govoplan-organizations.add_subunit.8256a8f7
-        </Button>
-      </div>,
-      ...renderUnitTreeNodes(unit.id, depth + 1, nextSeen)
-      ];
-    });
-  }
-
   function renderUnitsSection() {
     return (
       <div className="organizations-table-stack">
         <Card title="i18n:govoplan-organizations.organization_tree.e5bfb195" actions={<AdminIconButton label="i18n:govoplan-organizations.add_root_unit.1ef8a9f5" icon={<Plus size={16} aria-hidden="true" />} variant="primary" disabled={!canWriteUnits || busy} onClick={() => openUnitCreate()} />}>
-          <div className="organizations-tree-toolbar">
+          <div className="explorer-tree-toolbar">
             {selectedUnitId && <Button type="button" variant="ghost" disabled={busy} onClick={() => setSelectedUnitId("")}>i18n:govoplan-organizations.none.334c4a4c</Button>}
           </div>
-          <div className="organizations-tree-list">
-            {model.units.length ? renderUnitTreeNodes() : <p className="muted small-note">i18n:govoplan-organizations.no_units_found.eea2dd0c</p>}
-          </div>
+          {model.units.length ? (
+            <ExplorerTree
+              nodes={unitsByParentId.get("") ?? []}
+              getNodeId={(unit) => unit.id}
+              getNodeLabel={(unit) => unit.name}
+              getNodeChildren={(unit) => unitsByParentId.get(unit.id) ?? []}
+              activeId={selectedUnitId}
+              collapsible={false}
+              depth={0}
+              className="explorer-tree-scroll-region"
+              getNodeWrapStyle={(_unit, context) => ({ paddingLeft: `${Math.min(context.depth * 18, 72)}px` })}
+              onOpen={(unit) => setSelectedUnitId(unit.id)}
+              renderNodeContent={(unit) => (
+                <span className="explorer-tree-node-content">
+                  <strong>{unit.name}</strong>
+                  <small>{unitTypeById.get(unit.unit_type_id || "")?.name ?? "i18n:govoplan-organizations.no_unit_type.73e799f5"}</small>
+                </span>
+              )}
+              renderNodeActions={(unit) => (
+                <IconButton
+                  label="i18n:govoplan-organizations.add_subunit.8256a8f7"
+                  icon={<Plus size={16} aria-hidden="true" />}
+                  variant="ghost"
+                  disabled={!canWriteUnits || busy}
+                  onClick={() => addSubunit(unit)}
+                />
+              )}
+            />
+          ) : <p className="muted small-note">i18n:govoplan-organizations.no_units_found.eea2dd0c</p>}
         </Card>
         <Card title="i18n:govoplan-organizations.units.e14d0d92" actions={<AdminIconButton label="i18n:govoplan-organizations.add_unit.8fa12fb1" icon={<Plus size={16} aria-hidden="true" />} variant="primary" disabled={!canWriteUnits || busy} onClick={() => openUnitCreate()} />}>
           <DataGrid id="organizations-units" rows={model.units} columns={unitColumns} getRowKey={(row) => row.id} emptyText="i18n:govoplan-organizations.no_units_found.eea2dd0c" initialFit="container" />
diff --git a/webui/src/styles/organizations.css b/webui/src/styles/organizations.css
index f940ead..b4de1ee 100644
--- a/webui/src/styles/organizations.css
+++ b/webui/src/styles/organizations.css
@@ -50,51 +50,6 @@
   padding-top: 2px;
 }
 
-.organizations-tree-toolbar {
-  display: flex;
-  justify-content: flex-start;
-  margin-bottom: 12px;
-}
-
-.organizations-tree-list {
-  display: grid;
-  gap: 4px;
-  max-height: 640px;
-  overflow: auto;
-}
-
-.organizations-tree-row {
-  display: grid;
-  grid-template-columns: minmax(0, 1fr) auto;
-  align-items: center;
-  gap: 6px;
-}
-
-.organizations-tree-node {
-  display: grid;
-  gap: 2px;
-  width: 100%;
-  min-width: 0;
-  padding: 8px 10px;
-  border: 1px solid transparent;
-  border-radius: 7px;
-  background: transparent;
-  color: var(--text);
-  text-align: left;
-  cursor: pointer;
-}
-
-.organizations-tree-node:hover,
-.organizations-tree-node.active {
-  border-color: var(--line);
-  background: var(--surface-muted);
-}
-
-.organizations-tree-node span {
-  color: var(--muted);
-  font-size: 12px;
-}
-
 .organizations-field-note {
   margin: 8px 0 0;
   color: var(--muted);