Fix #34130

src/vs/base/parts/tree/browser/treeDefaults.ts

@@ -168,8 +168,8 @@ export class DefaultController implements _.IController {
 	}
 
 	protected onLeftClick(tree: _.ITree, element: any, eventish: ICancelableEvent, origin: string = 'mouse'): boolean {
-		const payload = { origin: origin, originalEvent: eventish };
 		const event = <mouse.IMouseEvent>eventish;
+		const payload = { origin: origin, originalEvent: eventish, didClickOnTwistie: this.isClickOnTwistie(event) };
 
 		if (tree.getInput() === element) {
 			tree.clearFocus(payload);

src/vs/workbench/browser/parts/views/customView.ts

@@ -34,6 +34,7 @@ import { LIGHT, FileThemeIcon, FolderThemeIcon } from 'vs/platform/theme/common/
 import { FileKind } from 'vs/platform/files/common/files';
 import { WorkbenchTreeController } from 'vs/platform/list/browser/listService';
 import { ViewletPanel, IViewletPanelOptions } from 'vs/workbench/browser/parts/views/panelViewlet';
+import { IMouseEvent } from 'vs/base/browser/mouseEvent';
 
 export class CustomTreeViewPanel extends ViewletPanel {
 
@@ -373,7 +374,7 @@ export class CustomTreeViewer extends Disposable implements ITreeViewer {
 	}
 
 	private onSelection({ payload }: any): void {
-		if (payload && payload.source === 'api') {
+		if (payload && (!!payload.didClickOnTwistie || payload.source === 'api')) {
 			return;
 		}
 		const selection: ITreeItem = this.tree.getSelection()[0];
@@ -586,6 +587,10 @@ class TreeController extends WorkbenchTreeController {
 		super({}, configurationService);
 	}
 
+	protected shouldToggleExpansion(element: ITreeItem, event: IMouseEvent, origin: string): boolean {
+		return element.command ? this.isClickOnTwistie(event) : super.shouldToggleExpansion(element, event, origin);
+	}
+
 	public onContextMenu(tree: ITree, node: ITreeItem, event: ContextMenuEvent): boolean {
 		event.preventDefault();
 		event.stopPropagation();