code: def get_node_type(dgtree):
      
      if is_leaf(dgtree):
          return TreeNodeTypes.leaf_node
  
      root_label = dgtree.label()
      if root_label == '':
          assert dgtree == DGParentedTree('', []), \
              "The tree has no root label, but isn't empty: {}".format(dgtree)
          return TreeNodeTypes.empty_tree
      elif root_label in NUCLEARITY_LABELS:
          return TreeNodeTypes.nuclearity_node
      else:
          assert isinstance(dgtree, (RSTTree, DGParentedTree)), type(dgtree)
          return TreeNodeTypes.relation_node
docs: Returns the type of the root node of a DGParentedTree.