src/vs/editor/contrib/gotoSymbol/browser/peek/referencesTree.ts/DataSource/hasChildren
class DataSource:	hasChildren(element: ReferencesModel | FileReferences | TreeElement): boolean {
		if (element instanceof ReferencesModel) {
			return true;
		}
		if (element instanceof FileReferences) {
			return true;
		}
		return false;
	}