code: def rebuild(cls, session, tree_id=None):
          
  
          trees = session.query(cls).filter_by(parent_id=None)
          if tree_id:
              trees = trees.filter_by(tree_id=tree_id)
          for tree in trees:
              cls.rebuild_tree(session, tree.tree_id)
docs: This function rebuid tree.
  
          Args:
              session (:mod:`sqlalchemy.orm.session.Session`): SQLAlchemy session
  
          Kwargs:
              tree_id (int or str): id of tree, default None
  
          Example:
  
          * :mod:`sqlalchemy_mptt.tests.TestTree.test_rebuild`