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 (data != null) {
					unmapElement(data, item);
				}
				item.setData(element);
				mapElement(element, item);
			}
			
			SafeRunnable.run(new UpdateItemSafeRunnable(item, element));
		}
	}
	/**
	 * Expands all nodes of the viewer's tree, starting with the root. This
	 * method is equivalent to <code>expandToLevel(ALL_LEVELS)</code>.
	 */
	public void expandAll() {
		expandToLevel(ALL_LEVELS);
	}
	/**
	 * Expands the root of the viewer's tree to the given level.
	 * 
	 * @param level
	 *            non-negative level, or <code>ALL_LEVELS</code> to expand all
	 *            levels of the tree
	 */
	public void expandToLevel(int level) {
		expandToLevel(getRoot(), level);
	}
	/**
	 * Expands all ancestors of the given element or tree path so that the given
	 * element becomes visible in this viewer's tree control, and then expands