public MultiMap<Value, T, List<T>> get(final KeyDefinition keyDefinition) {
        return tree.get(keyDefinition);
    }
@Test
    void testUpdateAge() throws Exception {
        final MultiMapChangeHandler changeHandler = mock(MultiMapChangeHandler.class);
        map.get(AGE).addChangeListener(changeHandler);

        toni.setAge(10);

        final MultiMap<Value, Person, List<Person>> age = map.get(AGE);

        assertThat(age.get(new Value(20))).doesNotContain(toni);
        assertThat(age.get(new Value(10))).contains(toni);
    }