digraph graph_02
{
graph [ label="Cluster set" rankdir="TB" ]

subgraph "cluster A"
{
graph [ label="Cluster A" rankdir="TB" ]

"A" [ color="green" ]
}

subgraph "cluster B"
{
graph [ label="Cluster B" rankdir="TB" ]

"B" [ color="green" ]
}

subgraph "cluster C"
{
graph [ label="Cluster C" rankdir="TB" ]

"C" [ color="green" ]
}

subgraph "cluster D"
{
graph [ label="Cluster D" rankdir="TB" ]

"D" [ color="green" ]
}
}
