src/vs/workbench/contrib/preferences/browser/tocTree.ts/TOCTreeModel/updateGroupCount
class TOCTreeModel:	private updateGroupCount(group: SettingsTreeGroupElement): void {
		group.children.forEach(child => {
			if (child instanceof SettingsTreeGroupElement) {
				this.updateGroupCount(child);
			}
		});

		const childCount = group.children
			.filter(child => child instanceof SettingsTreeGroupElement)
			.reduce((acc, cur) => acc + (<SettingsTreeGroupElement>cur).count!, 0);

		group.count = childCount + this.getGroupCount(group);
	}