[gpm]

For "proper" graphs, petgraph: https://crates.io/crates/petgraph

For trees without parent pointers: Just roll your own along the lines of the following. This fits nicely into rust's ownership semantics

    struct Node<T> {
        children: Vec<Node<T>>
    }

For trees with parent pointers, I'm not sure what's most common. Potentially Rc with Weak, potentially petgraph, maybe something else.