How to get data

Hi

I have below data 

I want to display like below

Group 2C , Group 2C(i)

Group 3C

Group 3D , Group 3D(i)

Group 3E

Group 3G

BALGroup bALGroup = new BALGroup();
                List<Group> objGroup = bALGroup.GetGroupList("Group");
                if (objGroup != null)
                {
                    List<string> GroupCollection = new List<string>();
                    foreach (var colum in objGroup)
                    {
                        GroupCollection.Add(colum.GroupName.ToString());
                    }
}

Thanks