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
Item[] items = getChildren(parent);
		for (int i = 0; i < items.length; i++) {
			Item item = items[i];
			Object data = item.getData();
			if (data != null && equals(data, element)) {
				return item;
			}
		}
		return null;
	}
	/**
	 * Recursively tries to find the given element.
	 * 
	 * @param parent
	 *            the parent item
	 * @param element
	 *            the element
	 * @return Widget
	 */
	private Widget internalFindItem(Item parent, Object element) {
		
		Object data = parent.getData();
		if (data != null) {
			if (equals(data, element)) {
				return parent;
			}
		}
		
		Item[] items = getChildren(parent);
		for (int i = 0; i < items.length; i++) {