Embedding dropdown menu with custom datagridview

Question

I have created a windows application which retrieve data from .dat file and convert it into datagridview(as per my requirement, it splits data into columns).Now column named "Grouptype" is there. I want to create a dropdownbox in that particular column. and it should be filled with the existing data of that column.

E.g. if there are 5 different values for Grouptype column then the dropdownbox should be filled by those values. and if i add any new row and grouptype column has any new value then it should be allowed to enter.

 

``public static SortableBindingList<User> LoadUserListFromBkpFile(string path)

   {

      var users = new SortableBindingList<User>();

      char[] delimiterChars = { '|' };

      foreach (var linedata in File.ReadAllLines(path))

     {

         string[] words = linedata.Split(delimiterChars);

         if (words.Count() < 10)

         {

            return users;

         }

         if (words[0].Trim() != "")

         {

            users.Add(new User

            {

                  LineNumber = int.Parse(words[0]),

                  GroupType = words[1],

                  CountyCode = words[2],

                  County = words[3],

                  Payee = words[4],

                  Address1 = words[5],

                  Address2 = words[6],

                  City = words[7],

                  State = words[8],

                  ZipCode = words[9]

               });

            }

         }

      return users;

}

I don't know how to add dropdownbox with this. and fill it with existing data at run time.