public Stream<ItemSet> stream() {
        return StreamSupport.stream(spliterator(), false);
    }
@Test
    public void testPima() {
        System.out.println("pima");

        FPTree tree = FPTree.of(20, () -> ItemSetTestData.read("transaction/pima.D38.N768.C2"));
        TotalSupportTree ttree = new TotalSupportTree(tree);
        assertEquals(1803, ttree.stream().count());
    }