Add following to TreeView

- Events to listen to when an element is expanded/collapsed
- Property to access selected elements

src/vs/vscode.d.ts

@@ -5870,6 +5870,21 @@ declare module 'vscode' {
 	 */
 	export interface TreeView<T> extends Disposable {
 
+		/**
+		 * Event that is fired when an element is expanded
+		 */
+		readonly onDidExpandElement: Event<T>;
+
+		/**
+		 * Event that is fired when an element is collapsed
+		 */
+		readonly onDidCollapseElement: Event<T>;
+
+		/**
+		 * Currently selected elements.
+		 */
+		readonly selectedElements: T[];
+
 		/**
 		 * Reveal an element. By default revealed element is selected.
 		 *

src/vs/workbench/api/node/extHostTreeViews.ts

@@ -49,6 +49,9 @@ export class ExtHostTreeViews implements ExtHostTreeViewsShape {
 		}
 		const treeView = this.createExtHostTreeViewer(viewId, options.treeDataProvider);
 		return {
+			get onDidCollapseElement() { return treeView.onDidCollapseElement; },
+			get onDidExpandElement() { return treeView.onDidExpandElement; },
+			get selectedElements() { return treeView.selectedElements; },
 			reveal: (element: T, options?: { select?: boolean }): Thenable<void> => {
 				return treeView.reveal(element, options);
 			},