code: def convert(cls, tree):
          
  
          if isinstance(tree, Tree):
              children = [cls.convert(child) for child in tree]
              if isinstance(tree, MetricalTree):
                  return cls(tree._cat, children, tree._dep, tree._lstress)
              elif isinstance(tree, DependencyTree):
                  return cls(tree._cat, children, tree._dep)
              else:
                  return cls(tree._label, children)
          else:
              return tree
docs: Convert a tree between different subtypes of Tree.  ``cls`` determines
          which class will be used to encode the new tree.
  
          :type tree: Tree
          :param tree: The tree that should be converted.
          :return: The new Tree.