Bug 161086 [Viewers] performance problem in AbstractTreeViewer.internalExpandToLevel
If you expand to ALL_LEVELS, internalExpandToLevel will call createChildren even if the element has no children, i.e. it does not check if the element is expandable. Found this while experimenting with the Quick Access feature (enter "con", then delete all three characters one at a time).
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/AbstractTreeViewer.java
* @param sorter
	 *            the sorter
	 * @return the tree path that should be used as the parent path for the
	 *         given widget and sorter
	 */
	private TreePath internalGetSorterParentPath(Widget parent,
			ViewerComparator comparator) {
		TreePath path;
		if (comparator instanceof TreePathViewerSorter
				&& parent instanceof Item) {
			Item item = (Item) parent;
			path = getTreePathFromItem(item);
		} else {
			path = null;
		}
		return path;
	}
	/**
	 * Compare the two elements using the given sorter. If the sorter is a
	 * {@link TreePathViewerSorter}, the provided tree path will be used. If
	 * the tree path is null and the sorter is a tree path sorter, then the
	 * elements are root elements
	 * 
	 * @param sorter
	 *            the sorter
	 * @param parentPath
	 *            the path of the elements' parent
	 * @param e1
	 *            the first element
	 * @param e2