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
}
	private void internalCollectVisibleExpanded(ArrayList result, Widget widget) {
		Item[] items = getChildren(widget);
		for (int i = 0; i < items.length; i++) {
			Item item = items[i];
			if (getExpanded(item)) {
				Object data = item.getData();
				if (data != null) {
					result.add(data);
				}
				
				
				internalCollectVisibleExpanded(result, item);
			}
		}
	}
	/**
	 * Returns the tree path for the given item.
	 * 
	 * @since 3.2
	 */
	protected TreePath getTreePathFromItem(Item item) {
		LinkedList segments = new LinkedList();
		while (item != null) {
			Object segment = item.getData();
			Assert.isNotNull(segment);
			segments.addFirst(segment);
			item = getParentItem(item);
		}
		return new TreePath(segments.toArray());