我需要在句子的依赖树中获取给定节点的子节点或父节点。怎么可能？例如，在下面的代码中，如何获取“study”的父节点？：
sentence = 'I am interested in NLP and want to have more study in this field'
result = list(dependency_parser.raw_parse(sentence))
dep_tree_dot_repr = [parse for parse in result][0].to_dot()
source = Source(dep_tree_dot_repr, filename="dep_tree", format="png")
source.view()