In Ocaml, the function "compress" takes a tree and converts it to a list of custom type comp using postorder traversal.

Write a function "decompress" that restores the list back to a tree. $($Example at bottom.$)$

type 'a tree $=$

$|$ Node of $\text{'}$a $*$ 'a tree $*$ 'a tree

$|$ Leaf

type 'a comp $=$

$|$ No of $\text{'}$a

$|$ Le

EXAMPLE

let t $=$Node $(50,$ Leaf, Node $(75,$Node $(50,$Leaf, Leaf$),$ Node $(125,$Leaf, Leaf$)))$

let co $=$ compress t;;

$(*$ 'a flat list: $[$Le; Le; Le; No $50$; Le; Le; No $125$; No $75$; No $50]*)$

let deco $=$ decompress co;;

$(*$ 'a tree: Node $(50,$ Leaf, Node $(75,$Node $(50,$Leaf, Leaf$),$ Node $(125,$Leaf, Leaf$)))*)$