To bind country, state, city

<data>
  <Country id="1" name="India" />
  <Country id="2" name="Australia" />
  <Country id="3" name="USA" />
  <State id="1" name="Maharastra" cid="1" />
  <State id="2" name="West Bengal" cid="1" />
  <State id="3" name="Orissa" cid="1" />
  <State id="4" name="Melbourne" cid="2" />
  <State id="5" name="New Jersy" cid="3" />
  <City id="1" name="Mumbai" sid="1" />
  <City id="2" name="Pune" sid="1" />
  <City id="3" name="Kolkata" sid="2" />
  <City id="4" name="Kharagpur" sid="2" />
  <City id="5" name="Bhubaneswar" sid="3" />
  <City id="6" name="Cuttack" sid="3" />
  <City id="7" name="AusCity1" sid="4" />
  <City id="8" name="USACity2" sid="5" />
</data>

<div>
        <asp:DropDownList ID="DdlCountry" runat="server" AutoPostBack="True" 
            onselectedindexchanged="DdlCountry_SelectedIndexChanged">
        </asp:DropDownList>
        <asp:DropDownList ID="DdlState" runat="server" AutoPostBack="True" 
            onselectedindexchanged="DdlState_SelectedIndexChanged">
        </asp:DropDownList>
        <asp:DropDownList ID="DdlCity" runat="server">
        </asp:DropDownList>
</div>

public static DataSet ds;
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!Page.IsPostBack)
        {
            ds = new DataSet();
            ds.ReadXml(Server.MapPath("~/XMLFile.xml"));
            BindCountry();
        }
    }

    public void BindCountry()
    {
        DdlCountry.DataTextField = "name";
        DdlCountry.DataValueField = "id";
        DdlCountry.DataSource = ds.Tables["Country"];
        DdlCountry.DataBind();
        BindState(DdlCountry.SelectedValue);
    }

    public void BindState(string cid)
    {
        DdlState.DataTextField = "name";
        DdlState.DataValueField = "id";
        DataView dv = new DataView(ds.Tables["State"]);
        dv.RowFilter = "cid = " + cid;
        DdlState.DataSource = dv.ToTable();
        DdlState.DataBind();
        BindCity(DdlState.SelectedValue);
    }

    public void BindCity(string sid)
    {
        DdlCity.DataTextField = "name";
        DdlCity.DataValueField = "id";
        DataView dv = new DataView(ds.Tables["City"]);
        dv.RowFilter = "sid = " + sid;
        DdlCity.DataSource = dv.ToTable();
        DdlCity.DataBind();

    }

    protected void DdlCountry_SelectedIndexChanged(object sender, EventArgs e)
    {
        BindState(DdlCountry.SelectedValue);
    }

    protected void DdlState_SelectedIndexChanged(object sender, EventArgs e)
    {
        BindCity(DdlState.SelectedValue);
    }