public boolean isBinaryTreeABST(Node head) {
        if (head != null) {
            if (head.left != null) {
                if ((Integer) head.left.value > (Integer) head.value) return false;
            }
            if (head.right != null) {
                if ((Integer) head.right.value < (Integer) head.value) return false;
            }
        }

        if (head.left != null)
            isBinaryTreeABST(head.left) ;
        if (head.right != null)
            isBinaryTreeABST(head.right);

        return true;

    }