<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _create_graph(structure_dict):
 """Creates pydot graph from the pipeline structure dict. Args: structure_dict (dict):
 dict returned by step.upstream_structure Returns: graph (pydot.Dot):
 object representing upstream pipeline structure (with regard to the current Step). """

    graph = pydot.Dot()
    for node in structure_dict['nodes']:
        graph.add_node(pydot.Node(node))
    for node1, node2 in structure_dict['edges']:
        graph.add_edge(pydot.Edge(node1, node2))
    return graph