Suppose your `Tree` is an array of `Nodes` sorted in whatever traversal order is expected to be good. Edges are fully defined as pairs of indices (Node[A] -> Node[B] means you need to know just A and B): Nodes can contain their own upstream indices.

If you need per-traversal state per node (such as visited status or intermediate dataflow), it's very handy to allocate another flat array for that and use the node indices.

I've looked into this in a compiler setting, transforming ASTs and intermediate representations.