src/vs/workbench/browser/parts/views/treeView.ts/TreeView/updateCollapseAllToggle
class TreeView:	private updateCollapseAllToggle() {
		if (this.showCollapseAllAction) {
			this.collapseAllToggleContext.set(!!this.root.children && (this.root.children.length > 0) &&
				this.root.children.some(value => value.collapsibleState !== TreeItemCollapsibleState.None));
		}
	}