Solve using Ocaml

let rec tree_fold (t: 'a tree) (u: 'b) (f: 'a -> 'b -> 'b -> 'b) = match t with | Leaf -> u | Node (v, l, r) -> f v (tree_fold l u f) (tree_fold r u f)

Implement the function tree_map : a tree -> (a -> b) -> b tree that returns a tree with the same structure as the original tree, but with the given function applied to every node. Use tree_fold. Do not use recursion.