Populate DropDownList using Multi Dimensional array in ASP.Net

How can i read multiple column values into an array list? I am trying to read a list of category names and category ids from database into an array list; i am then binding these values into drop-down list. With my current code, i am able to do with one column only but would like to pull both cat_name and cat_id so how can i do that?

aspx

<asp:DropDownList ID="DropDownList1" runat="server"  DataTextField="ct_name" DataValueField="ct_id" AppendDataBoundItems="true">
            <asp:ListItem Value="-1">Select</asp:ListItem>
            </asp:DropDownList>

code behind

 private ArrayList GetDummyData()
 {
     ArrayList arr = new ArrayList();
     string strConn = ConfigurationManager.ConnectionStrings["myCon"].ConnectionString.ToString();
     SqlConnection con = new SqlConnection(strConn);
     con.Open();
     SqlCommand cmd = new SqlCommand("select distinct ct_name, cat_id from [myTable].[dbo].[categories]", con);
     SqlDataReader objDR = cmd.ExecuteReader();

     if (objDR != null) {
         while (objDR.Read())
         {
             //fill arraylist
             arr.Add(objDR["ct_name"]);
         }
     }

     con.Close();
     return arr;
 }

 private void FillDropDownList(DropDownList ddl)
 {
     ArrayList arr = GetDummyData();
     foreach (string item in arr)
     {
         ddl.Items.Add(item);
     }
}