Add fileds in a list after groupby linq

public static IEnumerable<IGrouping<TKey, TElement>> GroupBy<TSource, TKey, TElement>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector, Func<TSource, TElement> elementSelector)
{
    return source.GroupBy(keySelector, elementSelector, EqualityComparer<TKey>.Default);
}
 
public static IEnumerable<IGrouping<TKey, TElement>> GroupBy<TSource, TKey, TElement>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector, Func<TSource, TElement> elementSelector, IEqualityComparer<TKey> comparer)
{
    return new GroupedEnumerable<TSource, TKey, TElement>(source, keySelector, elementSelector, comparer);
}