OCaml tree insert

gistfile1.ml

 tree =
  | Leaf of int option
  | Node of int * tree * tree

let rec insert tree i = match tree with
  | Leaf (None)   -> Leaf (Some i)
  | Leaf (Some y) ->
    if (i = y) then tree
    else (if (i < y) then
            (* 
                 insert (e.g.,) 10 into 20
                             20
                  10 --->   /
                           10
             *)
            Node(i,(Leaf (Some y)),Leaf None)
          else
            (* 
                 insert (e.g.,) 20 into 10
                             20
                  20 --->   /
                           10
             *)
            Node(y,(Leaf (Some i)), Leaf (None)))
  | Node (y,t1,t2) ->
    if (i = y) then tree
    else (if (i < y) then
            (* 
                 insert (e.g.,) 5 into 
                      10
                     /  \    
                    t1  t2  
             *)
            Node(y,insert t1 i,t2)
          else
            (* Symmetric operation on right side  *)
            Node (y,t1,insert t2 i))