Add elements in 'a tree in Ocaml -

so, here problem.. need write function add elements in tree , binary tree, must organized. problem in how tree defined. have tree:

type 'a tree = {   mutable cont:'a;   mutable left:'a bin_tree;   mutable right:'a bin_tree   }   , 'a bin_tree =    empty   |node of 'a bin_tree;; 

so, when write function add elements in tree says tree of type 'a tree , using function 'a bin_tree.

i tried lot of different ways write function , same error. function used last is:

let rec dodajvdrevo x = function empty -> node{cont=x; left=empty; right=empty} |node{cont; left; right} -> if x < cont node{cont; left= dodajvdrevo x left; right} else if x > cont node{cont; left; right = dodajvdrevo x right} else node{cont; left; right};; 

please me , give clues.

thank you!

the node constructor should take 'a tree instead of 'a bin_tree.