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
selection = new TreeSelection(treePath);
				
			} else {
				selection = getSelection();
				updateSelection(selection);
			}
			fireDoubleClick(new DoubleClickEvent(this, selection));
		}
	}
	/**
	 * Handles a tree collapse event from the SWT widget.
	 * 
	 * @param event
	 *            the SWT tree event
	 */
	protected void handleTreeCollapse(TreeEvent event) {
		if (event.item.getData() != null) {
			fireTreeCollapsed(new TreeExpansionEvent(this, event.item.getData()));
		}
	}
	/**
	 * Handles a tree expand event from the SWT widget.
	 * 
	 * @param event
	 *            the SWT tree event
	 */
	protected void handleTreeExpand(TreeEvent event) {
		if (!(getContentProvider() instanceof ILazyTreeContentProvider)) {
			createChildren(event.item);
		}