Bug 305739 [viewers] #expandToLevel(Object, level) retrieves all children when virtual
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/AbstractTreeViewer.java
if (parent == null) {
			return null;
		}
		Item[] siblings = getItems(parent);
		if (siblings != null) {
			if (siblings.length <= 1) {
				return getNextItem(parent, false);
			}
			for (int i = 0; i < siblings.length; i++) {
				if (siblings[i] == item && i < (siblings.length - 1)) {
					return siblings[i + 1];
				}
			}
		}
		return getNextItem(parent, false);
	}
	/**
	 * Returns the parent item of the given item in the tree, or
	 * <code>null</code> if there is no parent item.
	 *
	 * @param item
	 *            the item
	 * @return the parent item, or <code>null</code> if none
	 */
	protected abstract Item getParentItem(Item item);
	/**
	 * Returns the item before the given item in the tree, or <code>null</code>
	 * if there is no previous item.
	 *
	 * @param item