I think this kind of a case of selecting a data representation that matches what you want to do with it, the natural ordering of a tree turned in to a seq is going to be pre-order. If your data was in a dependency graph format instead of a tree of objects, different topological sorts would yield pre or post order iterations

sorry, the tree to graph thing misses what I was going for, the tree is of course already a graph, just when I think dep graph, I think of a structure like {a #{b c} b #{c} c 3{}} the difference being it is flattened

My tree lacks identity, but I did consider that, and still am.