private static <T> void append(@NotNull TreeMap<String, Collection<T>> map,
                                 @NotNull String key,
                                 @NotNull Collection<? extends T> values) {
    map.computeIfAbsent(key, k -> new HashSet<>()).addAll(values);
  }
private static <T> void append(@NotNull TreeMap<String, Collection<T>> map,
                                 @NotNull String key,
                                 @NotNull Collection<? extends T> values)