public MultiMap<Value, T, List<T>> get(final KeyDefinition keyDefinition) {
        return tree.get(keyDefinition);
    }
@Test
    void testRetract() throws Exception {
        toni.uuidKey.retract();

        assertThat(map.get(UUIDKey.UNIQUE_UUID).keySet()).containsExactlyInAnyOrder(eder.uuidKey.getSingleValue(), michael.uuidKey.getSingleValue());
        
        MultiMap<Value, Person, List<Person>> nameMap = map.get(KeyDefinition.newKeyDefinition()
                        .withId("name")
                        .build());
        
        assertThat(nameMap.keySet()).extracting(x -> x.getComparable()).containsExactly("Eder", "Michael");
        
        MultiMap<Value, Person, List<Person>> ageMap = map.get(KeyDefinition.newKeyDefinition()
                        .withId("age")
                        .build());
        
        assertThat(ageMap.keySet()).extracting(x -> x.getComparable()).containsExactly(20, 30);
        
    }