code: def add_child(graph, child_id, child_label, parent_id, colour):
      
      node = pydot.Node(child_id, style="filled", fillcolor=colour, label=child_label, shape="polygon", fontname=FONT)
      graph.add_node(node)
      graph.add_edge(pydot.Edge(parent_id, node))
docs: http://www.graphviz.org/doc/info/shapes.html#polygon