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
if (parent != null) {
				Widget pw = internalExpand(parent, false);
				if (pw != null) {
					
					createChildren(pw);
					Object element = internalToElement(elementOrPath);
					w = internalFindChild(pw, element);
					if (expand && pw instanceof Item) {
						
						Item item = (Item) pw;
						LinkedList toExpandList = new LinkedList();
						while (item != null && !getExpanded(item)) {
							toExpandList.addFirst(item);
							item = getParentItem(item);
						}
						for (Iterator it = toExpandList.iterator(); it
								.hasNext();) {
							Item toExpand = (Item) it.next();
							setExpanded(toExpand, true);
						}
					}
				}
			}
		}
		return w;
	}
	/**
	 * If the argument is a tree path, returns its last segment, otherwise
	 * return the argument
	 *