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
removeAll(tree);
				tree.setData(getRoot());
				internalInitializeTree(tree);
				if (useRedraw) {
					tree.setRedraw(true);
				}
			}
		});
	}
	/**
	 * @param tree
	 */
	protected void internalInitializeTree(Control tree) {
		createChildren(tree);
		internalExpandToLevel(tree, expandToLevel);
	}
	/**
	 * Recursively collapses the subtree rooted at the given widget to the given
	 * level.
	 * <p>
	 * </p>
	 * Note that the default implementation of this method does not call
	 * <code>setRedraw</code>.
	 * 
	 * @param widget
	 *            the widget
	 * @param level
	 *            non-negative level, or <code>ALL_LEVELS</code> to collapse
	 *            all levels of the tree
	 */