def tree(self):
        node = self.root

        word = node['word']
        deps = sorted(chain.from_iterable(node['deps'].values()))
        return Tree(word, [self._tree(dep) for dep in deps])
Starting with the ``root`` node, build a dependency tree using the NLTK
dataset/ETHPy150Open nltk/nltk/nltk/parse/dependencygraph.py/DependencyGraph.tree