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
*            the element or tree path
	 * @return the items for that element
	 */
	private Widget[] internalFindItems(Object parentElementOrTreePath) {
		Widget[] widgets = findItems(parentElementOrTreePath);
		if (parentElementOrTreePath instanceof TreePath) {
			TreePath path = (TreePath) parentElementOrTreePath;
			Widget w = internalFindItem(path);
			if (w == null) {
				widgets = new Widget[] {};
			} else {
				widgets = new Widget[] { w };
			}
		} else {
			widgets = findItems(parentElementOrTreePath);
		}
		return widgets;
	}
	/**
	 * Return the item at the given path or <code>null</code>
	 * 
	 * @param path
	 *            the path
	 * @return the item at that path TODO could probably do better than this
	 */
	private Widget internalFindItem(TreePath path) {
		Widget[] widgets = findItems(path.getLastSegment());
		for (int i = 0; i < widgets.length; i++) {
			Widget widget = widgets[i];
			if (widget instanceof Item) {