Hi nauna,

Check this example. Now please take its reference and correct your code.

HTML

<form id="form1" runat="server">
    <div>
        <ul id="menu"></ul>
    </div>
</form>
<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
<script type="text/javascript" src="https://ajax.aspnetcdn.com/ajax/jquery.ui/1.8.9/jquery-ui.js"></script>
<link rel="stylesheet" type="text/css" href="https://ajax.aspnetcdn.com/ajax/jquery.ui/1.8.9/themes/blitzer/jquery-ui.css" />
<script type="text/javascript">
    $(function () {
        $('ul').menu();
        $.ajax({
            url: "Handler.ashx",
            method: 'GET',
            dataType: 'json',
            contentType: "application/json; charset=utf-8",
            success: function (data) {
                $.each(data, function () {
                    var li = $('<li value="' + this.Id + '">' + this.MenuText + '</li>');
                    if (!this.Active) {
                        li.addClass('ui-state-disabled');
                    }
                    li.appendTo($('#menu'));
                });
            }
        });

        $('body').on('mouseenter', 'ul li', function () {
            var menu = $(this);
            $.ajax({
                url: "Handler.ashx?ParentId=" + $(this).attr('value'),
                method: 'GET',
                dataType: 'json',
                contentType: "application/json; charset=utf-8",
                success: function (data) {
                    var ul = $('<ul></ul>').empty();
                    $.each(data, function () {
                        var li = $('<li value="' + this.Id + '">' + this.MenuText + '</li>');
                        if (!this.Active) {
                            li.addClass('ui-state-disabled');
                        }
                        li.appendTo($(ul));
                    });
                    $(ul).appendTo($(menu));
                }
            });
        });

        $('body').on('mouseleave', 'ul li', function () {
            $(this).find('ul').remove();
        });
    });
</script>

Generic Handler

C#

<%@ WebHandler Language="C#" Class="Handler" %>

using System;
using System.Web;
using System.Collections.Generic;
using System.Data;
using System.Web.Script.Serialization;

public class Handler : IHttpHandler
{
    public void ProcessRequest(HttpContext context)
    {
        int id = 0;
        int.TryParse(context.Request.QueryString["ParentId"], out id);

        List<Menu> menus = GetMenus(id);
        JavaScriptSerializer se = new JavaScriptSerializer();
        context.Response.ContentType = "text/plain";
        context.Response.Write(se.Serialize(menus));
    }

    public static List<Menu> GetMenus(int parent)
    {
        List<Menu> menus = new List<Menu>();
        DataRow[] drs = GetData().Select("ParentId=" + parent);
        foreach (DataRow dr in drs)
        {
            Menu menu = new Menu();
            menu.Id = Convert.ToInt32(dr["Id"]);
            menu.MenuText = dr["MenuText"].ToString();
            menu.ParentId = Convert.ToInt32(dr["ParentId"]);
            menu.Active = Convert.ToBoolean(dr["Active"]);
            menus.Add(menu);
        }

        return menus;
    }

    public static DataTable GetData()
    {
        DataTable dt = new DataTable();
        dt.Columns.AddRange(new DataColumn[4] {
            new DataColumn("Id",typeof(int)),
            new DataColumn("MenuText",typeof(string)),
            new DataColumn("ParentId",typeof(int)),
            new DataColumn("Active",typeof(bool)) });
        dt.Rows.Add(1, "USA", 0, 1);
        dt.Rows.Add(2, "India", 0, 1);
        dt.Rows.Add(3, "Australia", 0, 1);
        dt.Rows.Add(5, "Virginia", 1, 1);
        dt.Rows.Add(6, "Maryland", 1, 1);
        dt.Rows.Add(7, "AP", 2, 1);
        dt.Rows.Add(8, "MP", 2, 1);
        dt.Rows.Add(9, "Karnataka", 2, 1);
        dt.Rows.Add(10, "Bangalore", 9, 1);
        dt.Rows.Add(11, "Mangalore", 9, 1);
        dt.Rows.Add(12, "Mysore", 9, 0);

        return dt;
    }

    public class Menu
    {
        public int Id { get; set; }
        public string MenuText { get; set; }
        public int ParentId { get; set; }
        public bool Active { get; set; }
    }

    public bool IsReusable
    {
        get
        {
            return false;
        }
    }
}

VB.Net

<%@ WebHandler Language="VB" Class="Handler" %>

Imports System
Imports System.Web
Imports System.Collections.Generic
Imports System.Data
Imports System.Web.Script.Serialization

Public Class Handler : Implements IHttpHandler

    Public Sub ProcessRequest(ByVal context As HttpContext) Implements IHttpHandler.ProcessRequest
        Dim id As Integer = 0
        Integer.TryParse(context.Request.QueryString("ParentId"), id)
        Dim menus As List(Of Menu) = GetMenus(id)
        Dim se As JavaScriptSerializer = New JavaScriptSerializer()
        context.Response.ContentType = "text/plain"
        context.Response.Write(se.Serialize(menus))
    End Sub

    Public Shared Function GetMenus(ByVal parent As Integer) As List(Of Menu)
        Dim menus As List(Of Menu) = New List(Of Menu)()
        Dim drs As DataRow() = GetData().[Select]("ParentId=" & parent)

        For Each dr As DataRow In drs
            Dim menu As Menu = New Menu()
            menu.Id = Convert.ToInt32(dr("Id"))
            menu.MenuText = dr("MenuText").ToString()
            menu.ParentId = Convert.ToInt32(dr("ParentId"))
            menu.Active = Convert.ToBoolean(dr("Active"))
            menus.Add(menu)
        Next

        Return menus
    End Function

    Public Shared Function GetData() As DataTable
        Dim dt As DataTable = New DataTable()
        dt.Columns.AddRange(New DataColumn(3) {
                            New DataColumn("Id", GetType(Integer)),
                            New DataColumn("MenuText", GetType(String)),
                            New DataColumn("ParentId", GetType(Integer)),
                            New DataColumn("Active", GetType(Boolean))})
        dt.Rows.Add(1, "USA", 0, 1)
        dt.Rows.Add(2, "India", 0, 1)
        dt.Rows.Add(3, "Australia", 0, 1)
        dt.Rows.Add(5, "Virginia", 1, 1)
        dt.Rows.Add(6, "Maryland", 1, 1)
        dt.Rows.Add(7, "AP", 2, 1)
        dt.Rows.Add(8, "MP", 2, 1)
        dt.Rows.Add(9, "Karnataka", 2, 1)
        dt.Rows.Add(10, "Bangalore", 9, 1)
        dt.Rows.Add(11, "Mangalore", 9, 1)
        dt.Rows.Add(12, "Mysore", 9, 0)
        Return dt
    End Function

    Public Class Menu
        Public Property Id As Integer
        Public Property MenuText As String
        Public Property ParentId As Integer
        Public Property Active As Boolean
    End Class

    Public ReadOnly Property IsReusable() As Boolean Implements IHttpHandler.IsReusable
        Get
            Return False
        End Get
    End Property
End Class