如何在DOT图中设置固定的深度级别

digraph {
    A -> B;
    B -> C;
    C -> D [label="Level 3"];
}

digraph {
    A -> B [label="Level 2"];
    B -> C;
    C -> D [label="Level 3"];
}

digraph {
    A -> B [label="Level 2"];
    B -> C [label="Level 3"];
    C -> D [label="Level 4"];
}

digraph {
    A -> B;
    B -> C;
    C -> D [label="Level 3"];
}

digraph {
    node [shape=box];
    A [label="Level 1"];
    B [label="Level 2"];
    C [label="Level 3"];
    D [label="Level 4"];
}

digraph {
    node [shape=box];
    A [label="Level 1"];
    B [label="Level 2"];
    C [label="Level 3"];
    D [label="Level 4"];
    A -> B [ltail=clusternet