code: def get_tree_type(tree):
      
      if is_leaf_node(tree):
          return SubtreeType.leaf
  
      tree_type = tree.label().lower().split(':')[0]
      assert tree_type in SUBTREE_TYPES
      return tree_type
docs: Return the (sub)tree type: 'root', 'nucleus', 'satellite', 'text' or 'leaf'
  
      Parameters
      ----------
      tree : nltk.tree.ParentedTree
          a tree representing a rhetorical structure (or a part of it)