public static <K extends Comparable<? super K>, V> AbstractGroupExpression<Pair<K, V>, SortedMap<K, V>> sortedMap(Expression<K> key,
                                                                                                                      Expression<V> value) {
        return GMap.createSorted(QPair.create(key, value));
    }
Create a new aggregating map expression using a backing TreeMap

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