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
* 
	 * @param parent
	 *            the parent widget
	 * @param element
	 *            the element
	 * @param index
	 *            if non-negative, indicates the position to insert the item
	 *            into its parent
	 */
	protected void createTreeItem(Widget parent, Object element, int index) {
		Item item = newItem(parent, SWT.NULL, index);
		updateItem(item, element);
		updatePlus(item, element);
	}
	/**
	 * The <code>AbstractTreeViewer</code> implementation of this method also
	 * recurses over children of the corresponding element.
	 */
	protected void disassociate(Item item) {
		super.disassociate(item);
		
		
		
		if (usingElementMap()) {
			disassociateChildren(item);
		}
	}
	/**
	 * Disassociates the children of the given SWT item from their corresponding
	 * elements.