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
Object element = elementsOrPaths[i];
			if (equals(element, input)) {
				setInput(null);
				return;
			}
			Widget[] childItems = internalFindItems(element);
			for (int j = 0; j < childItems.length; j++) {
				Widget childItem = childItems[j];
				if (childItem instanceof Item) {
					Item parentItem = getParentItem((Item) childItem);
					if (parentItem != null) {
						parentItems.put(parentItem, parentItem);
					}
					disassociate((Item) childItem);
					childItem.dispose();
				}
			}
		}
		internalReconcileParentItems(parentItems);
	}
	/**
	 * @param parentItems
	 */
	private void internalReconcileParentItems(CustomHashtable parentItems) {
		Control tree = getControl();
		for (Enumeration e = parentItems.keys(); e.hasMoreElements();) {
			Item parentItem = (Item) e.nextElement();
			if (parentItem.isDisposed()) {
				continue;
			}