diff --git a/packages/trace-viewer/src/ui/uiModeView.tsx b/packages/trace-viewer/src/ui/uiModeView.tsx
index 045661bf71..16076936e5 100644
--- a/packages/trace-viewer/src/ui/uiModeView.tsx
+++ b/packages/trace-viewer/src/ui/uiModeView.tsx
@@ -77,6 +77,7 @@ export const UIModeView: React.FC<{}> = ({
   const [watchedTreeIds, setWatchedTreeIds] = React.useState<{ value: Set<string> }>({ value: new Set() });
   const runTestPromiseChain = React.useRef(Promise.resolve());
   const runTestBacklog = React.useRef<Set<string>>(new Set());
+  const [collapseAllCount, setCollapseAllCount] = React.useState(0);
 
   const inputRef = React.useRef<HTMLInputElement>(null);
 
@@ -199,6 +200,9 @@ export const UIModeView: React.FC<{}> = ({
           <ToolbarButton icon='play' title='Run all' onClick={() => runTests('bounce-if-busy', visibleTestIds)} disabled={isRunningTest || isLoading}></ToolbarButton>
           <ToolbarButton icon='debug-stop' title='Stop' onClick={() => sendMessageNoReply('stop')} disabled={!isRunningTest || isLoading}></ToolbarButton>
           <ToolbarButton icon='eye' title='Watch all' toggled={watchAll} onClick={() => setWatchAll(!watchAll)}></ToolbarButton>
+          <ToolbarButton icon='collapse-all' title='Collapse all' onClick={() => {
+            setCollapseAllCount(collapseAllCount + 1);
+          }} />
         </Toolbar>
         <TestList
           statusFilters={statusFilters}
@@ -212,7 +216,8 @@ export const UIModeView: React.FC<{}> = ({
           watchAll={watchAll}
           watchedTreeIds={watchedTreeIds}
           setWatchedTreeIds={setWatchedTreeIds}
-          isLoading={isLoading} />
+          isLoading={isLoading}
+          requestedCollapseAllCount={collapseAllCount} />
       </div>
     </SplitView>
   </div>;
@@ -304,9 +309,11 @@ const TestList: React.FC<{
   isLoading?: boolean,
   setVisibleTestIds: (testIds: Set<string>) => void,
   onItemSelected: (item: { testCase?: TestCase, location?: Location }) => void,
-}> = ({ statusFilters, projectFilters, filterText, testModel, runTests, runningState, watchAll, watchedTreeIds, setWatchedTreeIds, isLoading, onItemSelected, setVisibleTestIds }) => {
+  requestedCollapseAllCount: number,
+}> = ({ statusFilters, projectFilters, filterText, testModel, runTests, runningState, watchAll, watchedTreeIds, setWatchedTreeIds, isLoading, onItemSelected, setVisibleTestIds, requestedCollapseAllCount }) => {
   const [treeState, setTreeState] = React.useState<TreeState>({ expandedItems: new Map() });
   const [selectedTreeItemId, setSelectedTreeItemId] = React.useState<string | undefined>();
+  const [collapseAllCount, setCollapseAllCount] = React.useState(requestedCollapseAllCount);
 
   // Build the test tree.
   const { rootItem, treeItemMap, fileNames } = React.useMemo(() => {
@@ -334,6 +341,17 @@ const TestList: React.FC<{
 
   // Look for a first failure within the run batch to select it.
   React.useEffect(() => {
+    // If collapse was requested, clear the expanded items and return w/o selected item.
+    if (collapseAllCount !== requestedCollapseAllCount) {
+      treeState.expandedItems.clear();
+      for (const item of treeItemMap.keys())
+        treeState.expandedItems.set(item, false);
+      setCollapseAllCount(requestedCollapseAllCount);
+      setSelectedTreeItemId(undefined);
+      setTreeState({ ...treeState });
+      return;
+    }
+
     if (!runningState || runningState.itemSelectedByUser)
       return;
     let selectedTreeItem: TreeItem | undefined;
@@ -352,7 +370,7 @@ const TestList: React.FC<{
 
     if (selectedTreeItem)
       setSelectedTreeItemId(selectedTreeItem.id);
-  }, [runningState, setSelectedTreeItemId, rootItem]);
+  }, [runningState, setSelectedTreeItemId, rootItem, collapseAllCount, setCollapseAllCount, requestedCollapseAllCount, treeState, setTreeState, treeItemMap]);
 
   // Compute selected item.
   const { selectedTreeItem } = React.useMemo(() => {
diff --git a/packages/trace-viewer/vite.config.ts b/packages/trace-viewer/vite.config.ts
index e8df5c7081..ef7b15780a 100644
--- a/packages/trace-viewer/vite.config.ts
+++ b/packages/trace-viewer/vite.config.ts
@@ -44,7 +44,7 @@ export default defineConfig({
     rollupOptions: {
       input: {
         index: path.resolve(__dirname, 'index.html'),
-        watch: path.resolve(__dirname, 'uiMode.html'),
+        uiMode: path.resolve(__dirname, 'uiMode.html'),
         popout: path.resolve(__dirname, 'popout.html'),
       },
       output: {
diff --git a/tests/playwright-test/ui-mode-test-tree.spec.ts b/tests/playwright-test/ui-mode-test-tree.spec.ts
index 9231c0beab..f9e727e393 100644
--- a/tests/playwright-test/ui-mode-test-tree.spec.ts
+++ b/tests/playwright-test/ui-mode-test-tree.spec.ts
@@ -221,4 +221,24 @@ test('should update parametrized tests', async ({ runUITest, writeFiles }) => {
             ◯ test FR
             ◯ test LT
   `);
-});
\ No newline at end of file
+});
+
+test('should collapse all', async ({ runUITest }) => {
+  const { page } = await runUITest(basicTestTree);
+
+  await page.getByTestId('test-tree').getByText('suite').click();
+  await page.keyboard.press('ArrowRight');
+  await expect.poll(dumpTestTree(page), { timeout: 15000 }).toContain(`
+    ▼ ◯ a.test.ts
+        ◯ passes
+        ◯ fails
+      ▼ ◯ suite <=
+          ◯ inner passes
+          ◯ inner fails
+  `);
+
+  await page.getByTitle('Collapse all').click();
+  await expect.poll(dumpTestTree(page), { timeout: 15000 }).toContain(`
+    ► ◯ a.test.ts
+  `);
+});