I see what you mean. Try grouping siblings into subgraphs, and adjusting the length of edges between generations to approximate shells. You might try NetworkX

I see what you mean. Try grouping siblings into subgraphs, and adjusting the length of edges between generations to approximate shells. You might try NetworkX as well. I don't think it offers a better layout engine for you, but it supports graphviz and is awfully convenient for working with the graph itself.