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
/**
	 * This implementation of setSelectionToWidget accepts a list of elements or
	 * a list of tree paths.
	 */
	protected void setSelectionToWidget(List v, boolean reveal) {
		if (v == null) {
			setSelection(new ArrayList(0));
			return;
		}
		int size = v.size();
		List newSelection = new ArrayList(size);
		for (int i = 0; i < size; ++i) {
			Object elementOrTreePath = v.get(i);
			
			
			Widget w = internalExpand(elementOrTreePath, false);
			if (w instanceof Item) {
				newSelection.add(w);
			} else if (w == null && elementOrTreePath instanceof TreePath) {
				TreePath treePath = (TreePath) elementOrTreePath;
				Object element = treePath.getLastSegment();
				if (element != null) {
					w = internalExpand(element, false);
					if (w instanceof Item) {
						newSelection.add(w);
					}
				}
			}
		}
		setSelection(newSelection);