✅ how to remove duplicates?

var groupedAccessGroups = accessGroups
    .SelectMany(accessGroup => accessGroup.Compositions,
        (accessGroup, compositions) => (
            accessGroup.Id,
            accessGroup.Title,
            accessGroup.Description,
             Compositions: compositions
        ))                                                                                                     
    .Where( accessGroup => territoriesIDs.Contains( accessGroup.Compositions.TerritoryId ) )
    .GroupBy( accessGroup => accessGroup.Compositions.TerritoryId );