How to create an XML file from SQL

using System;
using System.Data;
using System.Windows.Forms;
using System.Xml;
using System.Data.SqlClient; 

namespace WindowsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            string connetionString = null;
            SqlConnection connection );
            SqlDataAdapter adapter ;
            DataSet ds = new DataSet();
            string sql = null;

            connetionString = "Data Source=servername;Initial Catalog=databsename;User ID=username;Password=password";
            connection = new SqlConnection(connetionString);
            sql = "select * from Product";
            try
            {
                connection.Open();
                adapter = new SqlDataAdapter(sql, connection);
                adapter.Fill(ds);
                connection.Close();
                ds.WriteXml("Product.xml");
                MessageBox.Show("Done");
            }
            catch (Exception ex)
            {
                MessageBox.Show (ex.ToString());

            }
        }
    }
}