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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_multi_causal_upstream(graph, nbunch: Union[BaseEntity, Iterable[BaseEntity]]):
 """Get the union of all the 2-level deep causal upstream subgraphs from the nbunch. :param pybel.BELGraph graph: A BEL graph :param nbunch: A BEL node or list of BEL nodes :return: A subgraph of the original BEL graph :rtype: pybel.BELGraph """

    result = get_upstream_causal_subgraph(graph, nbunch)
    expand_upstream_causal(graph, result)
    return result