🐛 fixes #21096

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

@@ -644,7 +644,7 @@ export class TreeNavigator implements INavigator<Item> {
 		if (!item) {
 			return null;
 		} else {
-			if (!item.isVisible() || !item.isExpanded() || item.lastChild === null) {
+			if (!(item instanceof RootItem) && (!item.isVisible() || !item.isExpanded() || item.lastChild === null)) {
 				return item;
 			} else {
 				return TreeNavigator.lastDescendantOf(item.lastChild);
@@ -718,15 +718,7 @@ export class TreeNavigator implements INavigator<Item> {
 	}
 
 	public last(): Item {
-		if (this.start && this.start.isExpanded()) {
-			this.item = this.start.lastChild;
-
-			if (this.item && !this.item.isVisible()) {
-				this.previous();
-			}
-		}
-
-		return this.item || null;
+		return TreeNavigator.lastDescendantOf(this.start);
 	}
 }
 

src/vs/base/parts/tree/test/browser/treeModel.test.ts

@@ -556,6 +556,15 @@ suite('TreeModel - TreeNavigator', () => {
 			done();
 		});
 	});
+
+	test('last()', () => {
+		return model.setInput(SAMPLE.AB).then(() => {
+			return model.expandAll([{ id: 'a' }, { id: 'c' }]).then(() => {
+				const nav = model.getNavigator();
+				assert.equal(nav.last().id, 'cb');
+			});
+		});
+	});
 });
 
 suite('TreeModel - Expansion', () => {