digraph virt {
    graph [nodesep=1.5, rankdir=BT];

    V [shape=plaintext, height=.1, fontsize=24];
    A [shape=plaintext, height=.1, fontsize=24];
    B [shape=plaintext, height=.1, fontsize=24];
    C [shape=plaintext, height=.1, fontsize=24];

    C -> B;
    C -> A;
    B -> V;
    A -> V;
}