src/vs/base/browser/ui/tree/asyncDataTree.ts/CompressibleAsyncDataTreeRenderer/renderTwistie
class CompressibleAsyncDataTreeRenderer:	renderTwistie(element: IAsyncDataTreeNode<TInput, T>, twistieElement: HTMLElement): boolean {
		if (element.slow) {
			twistieElement.classList.add(...Codicon.treeItemLoading.classNamesArray);
			return true;
		} else {
			twistieElement.classList.remove(...Codicon.treeItemLoading.classNamesArray);
			return false;
		}
	}