merge two table in one table

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;

public partial class TAT_merge2tablein1table : System.Web.UI.Page
{
    DataSet ds = new DataSet();
    public int totalcount_3;
    protected void Page_Load(object sender, EventArgs e)
    {
        // string domainUser = System.Security.Principal.WindowsIdentity.GetCurrent().Name.ToString();
        // string[] paramsLogin = domainUser.Split('\\');
        //Response.Write( paramsLogin[0].ToString());
        BindUserAccounts();
    }

    private void BindUserAccounts()
    {
        OfferDetails _OfferDetails = new OfferDetails();

        _OfferDetails._OfferDetailsCardId = "24";
        //this.CategotynameToMatch; "
        // SqlDataAdapter da = new SqlDataAdapter("select username,lastname from UserProfile ", con);
        ds = _OfferDetails.GetOfferDetails_AllFilter();
        int totalcount_1 = ds.Tables[0].Rows.Count;
        int totalcount_2 = ds.Tables[1].Rows.Count;
        totalcount_3 = totalcount_1 + 1;

        DataTable dt = new DataTable();
        DataColumn colString = new DataColumn("Categoryname");
        colString.DataType = System.Type.GetType("System.String");
        dt.Columns.Add(colString);

        DataColumn colString1 = new DataColumn("Categoryid");
        colString1.DataType = System.Type.GetType("System.String");
        dt.Columns.Add(colString1);

        //DataRow dataRow = dt.NewRow();
        //dataRow["Categoryname"] = "Dining";
        //dataRow["Categoryid"] = "8";
        //dt.Rows.Add(dataRow);

        // Dim i As Integer = 0
        //Dim table As DataTable = ds.Tables(0)
        //table.Columns.Add(New DataColumn("no", GetType(Integer)))
        //Dim rowcount As Integer = table.Rows.Count
        //Dim k As Integer = 1
        //While (i < rowcount)
        //    table.Rows(i)("no") = k
        //    i = i + 1
        //    k = k + 1

        //End While
        int i = 0;
        DataTable dt1 = ds.Tables[0];
        int rowcount = dt1.Rows.Count;
        int k = 1;
        DataTable dt2 = ds.Tables[1];
        int rowcount2 = dt2.Rows.Count;


        foreach (DataRow dr in dt1.Rows)
        {
            DataRow lLang = dt.NewRow();
            lLang["Categoryname"] = dr["CategotyName"].ToString();
            lLang["Categoryid"] = dr["pkCatId"].ToString();
            dt.Rows.Add(lLang);
        }
        foreach (DataRow dr in dt2.Rows)
        {
            DataRow lLang = dt.NewRow();
            lLang["Categoryname"] = dr["CategotyName"].ToString();
            lLang["Categoryid"] = dr["pkCatId"].ToString();
            dt.Rows.Add(lLang);
        }

        GridView1.DataSource = dt;
        GridView1.DataBind();

    }


}