public static <K, V, T, U> AbstractGroupExpression<Pair<K, V>, SortedMap<T, U>> sortedMap(GroupExpression<K, T> key,
                                                                                              GroupExpression<V, U> value,
                                                                                              Comparator<? super T> comparator) {
        return new GMap.Mixin<K, V, T, U, SortedMap<T, U>>(key, value, GMap.createSorted(QPair.create(key, value), comparator));
    }
Create a new aggregating map expression using a backing TreeMap using the given comparator

@param key key for the map entries
@param value value for the map entries
@param comparator comparator for the created TreeMap instances
@return wrapper expression
querydsl-core/src/main/java/com/querydsl/core/group/GroupBy.java