src/vs/base/browser/ui/tree/abstractTree.ts/AbstractTree/onLeftArrow
class AbstractTree:	private onLeftArrow(e: StandardKeyboardEvent): void {
		e.preventDefault();
		e.stopPropagation();

		const nodes = this.view.getFocusedElements();

		if (nodes.length === 0) {
			return;
		}

		const node = nodes[0];
		const location = this.model.getNodeLocation(node);
		const didChange = this.model.setCollapsed(location, true);

		if (!didChange) {
			const parentLocation = this.model.getParentNodeLocation(location);

			if (!parentLocation) {
				return;
			}

			const parentListIndex = this.model.getListIndex(parentLocation);

			this.view.reveal(parentListIndex);
			this.view.setFocus([parentListIndex]);
		}
	}