How do I place nodes on the same level in DOT?

Question

I want to render several trees simultaneously and place all root nodes and all leaf nodes on the same level.

Here\'s an example of what I\'m trying to do. Root nodes A a

Answer 1

The ideal structure is actually rank max and rank min. No need for a subgraph or any other shenanigans. GraphViz has explicit facilities for this.

With complex graphs, rank=same will often end up near the middle of the graph. If you mean top and bottom, say top and bottom.

digraph G { 

  rankdir = TB;

  A -> B;
  A -> C -> D;
  X -> Y;

  { rank=min; A; X; }
  { rank=max; B; D; Y; }

}