Adding values to a dropdown using AJAX

using System;
using System.Data;
using System.Data.SqlClient;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using Ganesh;

namespace MyAjaxSample
    {
    public partial class Testing : System.Web.UI.Page
        {
        public static string connectionString = (string)ConfigurationManager.AppSettings["ConnectionString"];
        public DataSet ds = new DataSet();
        DBClass MyClass = new DBClass();
        public SqlDataAdapter ObjSDA;
        protected void Page_Load(object sender, EventArgs e)
            {
            AjaxPro.Utility.RegisterTypeForAjax(typeof(Testing));
            if (!IsPostBack)
                {
                DropDownList1.DataSource = MyClass.GetDataSet("Select * from Testing");
                DropDownList1.DataTextField = "Name";
                DropDownList1.DataValueField = "ID";
                DropDownList1.DataBind();
                DropDownList1.Items.Add("--Select table--");
                DropDownList1.SelectedIndex = DropDownList1.Items.Count - 1;
                }
            }
        [AjaxPro.AjaxMethod]
        public DataSet Inserting(string Name)
            {
            SqlConnection myConnection = new SqlConnection(connectionString);
            string strQuery = "Insert into Testing Values('" + Name + "')";
            int res = MyClass.ExecuteQry(strQuery);
            ObjSDA = new SqlDataAdapter("Select * from Testing", myConnection);
            ObjSDA.Fill(ds);
            return ds;
            }
        }
    }