static int min = -1;
    static boolean flag = true;

    public static void inOrder(Node root){ 

        if(root.left != null){
            inOrder(root.left);
        }
        if(root.data <= min){
            flag = false;
        }
        min = root.data;
        if(root.right != null){
            inOrder(root.right);
        }
    }
    
    boolean checkBST(Node root) {
        inOrder(root);
        return flag;       
    }