More than 1 row in DataTable for shopping cart

 public partial class ShowProduct : System.Web.UI.Page
{
   public DataTable DT = new DataTable();



protected void Button1_Click(object sender, EventArgs e)
    {
            AddNewRow();
            GridView1.DataSource = (DataTable)Session["mySession"];
            GridView1.DataBind();             
    }
    private void AddNewRow()
    {
        int Artnr = Convert.ToInt32(Request.QueryString.Get("Artnr"));
        LuftcoPbrytfjader myProduct;

        using (KlippexDataContext kc = new KlippexDataContext())
        {
            myProduct = (from r in kc.LuftcoPbrytfjaders
                         where r.Artnr == Artnr
                         select r).Single();

            DataColumn MyColumn;

            MyColumn = new DataColumn("Artikelnummer");
            DT.Columns.Add(MyColumn);
            MyColumn = new DataColumn("Produktnamn");
            DT.Columns.Add(MyColumn);
            MyColumn = new DataColumn("Pris");
            DT.Columns.Add(MyColumn);



            DataRow MyRow = DT.NewRow();

            MyRow[0] = myProduct.Artnr;
            MyRow[1] = myProduct.Produktnamn;
            MyRow[2] = myProduct.Pris;

            DT.Rows.Add(MyRow);
            
            DT.AcceptChanges();

            
            Session["mySession"] = DT;
            
        }
    }






}