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

        FPTree tree = FPTree.of(1500, () -> ItemSetTestData.read("transaction/kosarak.dat"));
        TotalSupportTree ttree = new TotalSupportTree(tree);
        assertEquals(219725, ttree.stream().count());
    }