//summing the values in a int binTree

let rec sum   btree =
    match btree with
        | Leaf -> 0
        | Node ( r, left, right ) -> r + sum left + sum right

// number of nodes
let rec count   btree =
    match btree with
        | Leaf -> 0
        | Node ( r, left, right ) -> 1 + count left + count right

// depth of a tree
let rec depth   btree =
    match btree with
        | Leaf -> 0
        | Node ( r, left, right ) -> 1 + (max (depth left) ( depth right))