public Heap<T> insert(T item) {
        data.add(item);
        bubbleUp();
        return this;
    }
@Test
    public void insert() {
        Heap<Integer> h = new Heap<>(data, MIN);
        assertEquals("incorrect size", 10, h.size());
        h.insert(3);
        assertEquals("incorrect size", 11, h.size());
    }