using System;

using System.Data;

using System.Xml.Serialization;

using System.Xml;

​

public class Program

{

    public static void Main()

    {

        //inner datatable

        var dt2 = new InnerTable{TestOne = "Value1", TestTwo = "Value2"};

        //outer datatable

        DataTable dt = new DataTable();

        DataColumn dc1 = new DataColumn("Name");

        DataColumn dc2 = new DataColumn("Age");

        DataColumn dc3 = new DataColumn("Gender");

        DataColumn dc4 = new DataColumn("InnerDataTable", typeof (InnerTable));

        dt.Columns.Add(dc1);

        dt.Columns.Add(dc2);

        dt.Columns.Add(dc3);

        dt.Columns.Add(dc4);

        //adding of inner datatable to outer datatable

        dt.Rows.Add("John", "23", "Male", dt2);

        dt.Rows.Add("Gretchen", "25", "Female", dt2);

        dt.Rows.Add("Jordan", "28", "Male", dt2);

        DataSet ds = new DataSet();

        ds.Tables.Add(dt);

        string xml = ds.GetXml();

        Console.WriteLine(xml);

        Console.ReadLine();

    }

​

    public class InnerTable

    {

        public string TestOne { get; set; }

        public string TestTwo { get; set; }

    }

}