Delete a element in a tree in Haskell :     data BinaryTree a = Null | Node (BinaryTree a) a (BinaryTree a)
    deriving Show


      treeDelete :: (Ord a) => (BSTree a) -> a -> (BSTree a)
      treeDelete a btree = case btree of
        Null -> Null
        Node Null val Null
           |a==val -> Null
           |otherwise -> Node Null val Null
        Node left val right
               |a==val-> Node left Null right
               |otherwise -> (treeDelete a left) val (treeDelete a right)
   What I want to do is to takes a binary search tree, and an element, and removes it from the tree
(if it is present).
