✅ How to change property in tree-like objects?

var departmentsIds = _parameters.ShowSubjectsOfNestedDepartments
      ? await GetDepartmentsIdsWithNested()
      : _parameters.DepartmentIDs;

var groupedSubjects = ( await _subjectClient
      .GetByDepartmentsIds( departmentsIds )
      .Unwrap() )
      .GroupBy( x => x.Department.Title );

public class SubjectDto
{
   public string Id { get; set; }
   public DepartmentDigestDto Department { get; set; }
}

public class DepartmentDigestDto
{
    [JsonProperty( PropertyName = "id" )]
    [JsonRequired]
    public string Id { get; set; }

    [JsonProperty( PropertyName = "title" )]
    public string Title { get; set; }

    [JsonProperty( PropertyName = "parent_department_id" )]
    public string ParentDepartmentId { get; set; }
}