Fill dropdownlist using Cashcading style sheet in asp.net

HTML-- without parent id

<asp:DropDownList ID="ddl_block" runat="server"  >  </asp:DropDownList>

<asp:CascadingDropDown ID="Cascadingddl_block" runat="server" Category="SubDistrict" TargetControlID="ddl_block" LoadingText="Loading SubDistrict..." PromptText="---Select---" ServiceMethod="BindSubDitstrictdropdown" ServicePath="~/DropdownWebService.asmx"> </asp:CascadingDropDown>

WebService-

 [WebMethod(EnableSession = true)]

    public CascadingDropDownNameValue[] BindStatedropdown(string knownCategoryValues, string category)

    {

        StringDictionary countrydetails = AjaxControlToolkit.CascadingDropDown.ParseKnownCategoryValuesString(knownCategoryValues);

        DataTable dtSelectMethod = new DataTable();

        dtSelectMethod = Select_All_Data("mstAState", "*", "Active='1'", "StateName", "ASC");

        int Index = 0;

        List<CascadingDropDownNameValue> statedetails = new List<CascadingDropDownNameValue>();

        foreach (DataRow dtstaterow in dtSelectMethod.Rows)

        {

            string StateCode = dtstaterow["StateCode"].ToString();

            string StateName = dtstaterow["StateName"].ToString();

            statedetails.Add(new CascadingDropDownNameValue(StateName, StateCode));

        }

        return statedetails.ToArray();

    }                    

HTML-- with parent id

<asp:DropDownList ID="ddl_block" runat="server" ></asp:DropDownList>

<asp:CascadingDropDown ID="Cascadingddl_block" runat="server" Category="SubDistrict" TargetControlID="ddl_block" LoadingText="Loading SubDistrict..." PromptText="---Select---" ServiceMethod="BindSubDitstrictdropdown" ServicePath="~/DropdownWebService.asmx"   ParentControlID="ddl_district"> </asp:CascadingDropDown>

[WebMethod(EnableSession = true)]

    public CascadingDropDownNameValue[] BindClusterdropdown(string knownCategoryValues, string category)

    {

        string StateCode;

        StringDictionary StateCodedetails = AjaxControlToolkit.CascadingDropDown.ParseKnownCategoryValuesString(knownCategoryValues);

        StateCode = Convert.ToString(StateCodedetails["State"]);

        

        string clusternames = null;

        string clus = Session["clustercheck"].ToString();

        if (clus != "")

        {

            if (clus.Length == 6)

            {

                clusternames = "'" + clus + "'";

            }

            else

            {

                // clusternames = clus.Substring(0, clus.Length - 1);

                clusternames = clus;

            }

        }

        DataTable dtSelectMethod = new DataTable();

        string condition = "";

        if (clusternames == null)

        { condition = "StateCode='" + StateCode + "'"; }

        else { condition = " StateCode='" + StateCode + "' and ClusterCode in (" + clusternames + ") "; }

         

       // string 

        dtSelectMethod = Select_All_Data("mstBCluster", "*", condition, "ClusterName", "ASC");

        List<CascadingDropDownNameValue> regiondetails = new List<CascadingDropDownNameValue>();

        foreach (DataRow dtregionrow in dtSelectMethod.Rows)

        {

            string ClusterCode = dtregionrow["ClusterCode"].ToString();

            string ClusterName = dtregionrow["ClusterName"].ToString();

            regiondetails.Add(new CascadingDropDownNameValue(ClusterName, ClusterCode));

        }

        return regiondetails.ToArray();

    }