$graph = new Alom\Graphviz\Digraph('G');
$graph
    ->subgraph('cluster_1')
        ->attr('node', array('style' => 'filled', 'fillcolor' => 'blue'))
        ->node('A')
        ->node('B')
        ->edge(array('b0', 'b1', 'b2', 'b3'))
    ->end()
    ->edge(array('A', 'B', 'C'))
;
echo $graph->render();