✅ How to write special linq group by? How to shorten my code?

// returns Dictionary<string, string> and IEnumerable<string> as I said before
var departments = await GetDepartmentsWithNested();

// get subjects and than simple grouping 
var groupedSubjects = (await _subjectClient
    .GetByDepartmentsIds(departments.Item1.Keys)
    .Unwrap()
 .GroupBy(subject => (
    DepartmentId: subject.Department.Id,
    Title: departments.Item1[subject.Department.Id]));

// fill dataset with data
foreach(var group in groupedSubjects)
  foreach(var subject in group)
{
     dataSet.Staff.AddStaffRow(
        Title: subject.GetSubjectFullName(),
        AccessGroup: GetAccessGroupFormattedString(subject.AccessGroups),
        TabNumber: subject.Data.FromJson<SubjectData>()?.PersonnelNumber,
        Identifier: GetIdentifierFormattedString(subject.Identifiers),
        Department: group.Key.Title);
}

var anotherGroupedSubjects = (await _subjectClient
    .GetByDepartmentsIds(departments.Item2)
    .Unwrap()
 .GroupBy(subject => subject.Department.Title);

foreach(var group in anotherGroupedSubjects)
  foreach(var subject in group)
{
     dataSet.Staff.AddStaffRow(
        Title: subject.GetSubjectFullName(),
        AccessGroup: GetAccessGroupFormattedString(subject.AccessGroups),
        TabNumber: subject.Data.FromJson<SubjectData>()?.PersonnelNumber,
        Identifier: GetIdentifierFormattedString(subject.Identifiers),
        Department: group.Key);
}