src/vs/workbench/browser/parts/views/treeView.ts/AbstractTreeView/expand
class AbstractTreeView:	async expand(itemOrItems: ITreeItem | ITreeItem[]): Promise<void> {
		const tree = this.tree;
		if (tree) {
			itemOrItems = Array.isArray(itemOrItems) ? itemOrItems : [itemOrItems];
			await Promise.all(itemOrItems.map(element => {
				return tree.expand(element, false);
			}));
		}
	}