RectHV r = new RectHV(0, 0, 1, 1);
        Iterable<Point2D> set = kdtree.range(r);
        for (Point2D p:set) {
            StdOut.println("("+ p.x() + ", " + p.y() + ")");
            if (kdtree.contains(p)) {
                StdOut.println("kdtree contains it");
            }
            else  StdOut.println("kdtree does NOT contain it!");
        }