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
/**
	 * Constant indicating that all levels of the tree should be expanded or
	 * collapsed.
	 * 
	 * @see #expandToLevel
	 * @see #collapseToLevel
	 */
	public static final int ALL_LEVELS = -1;
	/**
	 * List of registered tree listeners (element type:
	 * <code>TreeListener</code>).
	 */
	private ListenerList treeListeners = new ListenerList();
	/**
	 * The level to which the tree is automatically expanded each time the
	 * viewer's input is changed (that is, by <code>setInput</code>). A value
	 * of 0 means that auto-expand is off.
	 * 
	 * @see #setAutoExpandLevel
	 */
	private int expandToLevel = 0;
	/**
	 * Safe runnable used to update an item.
	 */
	class UpdateItemSafeRunnable extends SafeRunnable {