digraph { node [ fontname = Courier ]
1 [ fillcolor = magenta style=filled shape=circle ]
2 [peripheries=2 shape=circle ]
3 [peripheries=2 shape=circle ]
4 [shape=circle ]
5 [shape=circle ]
6 [shape=circle ]

1 -> 2
1 -> 3
2 -> 4
2 -> 5
3 -> 5
3 -> 6
4 -> 4
4 -> 5
5 -> 5
5 -> 5
6 -> 5
6 -> 6

}