From Graphviz Clusters
digraph { node [shape=box style=filled fillcolor=bisque] 3 6 9 node[fillcolor=palegreen] 0 [label="Node\ne"] 1 [label="Node\na"] 2 [label="Node\nb"] 3 [label="Cluster\nX"] 4 [label="Node\nC"] 5 [label="Node\nD"] 6 [label="Cluster\nZ"] 7 [label="Node\nd"] 8 [label="Node\nf"] 9 [label="Cluster\nY"] 1 -> 2 [label="Links"] 1 -> 3 [label="Parent"] 2 -> 3 [label="Parent"] 4 -> 5 [label="Links"] 4 -> 6 [label="Parent"] 5 -> 6 [label="Parent"] 6 -> 3 [label="Parent"] 7 -> 8 [label="Links"] 7 -> 9 [label="Parent"] 8 -> 9 [label="Parent"] 7 -> 5 [label="Links"] 0 -> 9 [label="Links"] 6 -> 9 [label="Links"] }