code: public static Object getParent(TreeModel treeModel, Object node)
      {
          return getParent(treeModel, node, treeModel.getRoot());
      }
docs: Returns the parent of the given node in the given tree model.
  This parent may be <code>null</code>, if the given node is
  the root node (or not contained in the tree model at all).
  
  @param treeModel The tree model
  @param node The node
  @return The parent