code: public static DefaultMutableTreeNode findNode(
          TreeModel treeModel, Object userObject)
      {
          return findNode(treeModel, treeModel.getRoot(), userObject);
      }
docs: Returns the first node with the given user object in the tree with
  the given model. This assumes that the user object is stored
  in a DefaultMutableTreeNode.
  Returns <code>null</code> if no matching node is found.
  
  @param treeModel The tree model
  @param userObject The user object
  @return The node with the given user object, or <code>null</code>