Loop optimization (Multi level Menu) ASP.NET

I'm trying create a function to generate HTML file for multi-language menu. The code can work but only problem is its taking too long to compile. The flow is, this function will be called in the Global.asax file (process before start the program)

I suspect it caused by the looping process. So please advice me about the optimization. Thank you in advance. Here is the code.

 public static void GenerateMenu(string strPath)
{
    string[] tempCateHTML = new string[] { "_temp_menu_en.cshtml", "_temp_menu_bm.cshtml", "_temp_menu_ch.cshtml" }; //temporary file names
    string[] cateHTML = new string[] { "_menu_en.cshtml", "_menu_bm.cshtml", "_menu_ch.cshtml" };
    for (int i = 0; i < 3; i++)
    {

        using (EFContext ctx = new EFContext())
        {
            List<int> parentId = new List<int>();
            List<Category> parentCategory = ctx.Database.SqlQuery<Category>
                ("select CategoryId, category_name, category_nameBM, category_nameCH from dbo.lCategories where thread_parent = 0").ToList();

            StringWriter sWriter = new StringWriter();
            using (HtmlTextWriter wt = new HtmlTextWriter(sWriter))
            {
                 foreach (Category cate in parentCategory)
                {

                    string[] columnParent = new string[] { cate.Category_Name, cate.Category_NameBM, cate.Category_NameCH };
                    wt.RenderBeginTag(HtmlTextWriterTag.Li); //<li>
                    wt.AddAttribute(HtmlTextWriterAttribute.Href, "#");
                    wt.RenderBeginTag(HtmlTextWriterTag.A); //<a>
                    wt.Write(columnParent[i]);
                    wt.RenderEndTag();//</a>

                    wt.RenderBeginTag(HtmlTextWriterTag.Ul);//<ul>

                    List<Category> childCategoryL1 = ctx.Database.SqlQuery<Category>
                        ("select CategoryId, category_name, category_nameBM, category_nameCH from dbo.lCategories where thread_parent = {0}", cate.CategoryID).ToList();

                   foreach (Category root in childCategoryL1)
                    {
                        string[] columnChild1 = new string[] { root.Category_Name, root.Category_NameBM, root.Category_NameCH };
                        wt.RenderBeginTag(HtmlTextWriterTag.Li);//<li>
                        wt.AddAttribute(HtmlTextWriterAttribute.Href, "#");
                        wt.RenderBeginTag(HtmlTextWriterTag.A);//<a>
                        wt.Write(columnChild1[i]);
                        wt.RenderEndTag();//</a>

                        List<Category> childCategoryL2 = ctx.Database.SqlQuery<Category>
                            ("select CategoryId, category_name, category_nameBM, category_nameCH from dbo.lCategories where thread_parent = {0}", root.CategoryID).ToList();

                        if (childCategoryL2.Count > 0)
                        {
                            wt.RenderBeginTag(HtmlTextWriterTag.Ul);//<ul>

                            foreach (Category child1 in childCategoryL2)
                            {
                                string[] columnChild2 = new string[] { child1.Category_Name, child1.Category_NameBM, child1.Category_NameCH };
                                wt.RenderBeginTag(HtmlTextWriterTag.Li);//<li>
                                wt.AddAttribute(HtmlTextWriterAttribute.Href, "#");
                                wt.RenderBeginTag(HtmlTextWriterTag.A);//<a>
                                wt.Write(columnChild2[i]);
                                wt.RenderEndTag();//</a>

                                List<Category> childCategoryL3 = ctx.Database.SqlQuery<Category>
                                    ("select CategoryId, category_name, category_nameBM, category_nameCH from dbo.lCategories where thread_parent = {0}", child1.CategoryID).ToList();

                                if (childCategoryL3.Count > 0)
                                {
                                    wt.RenderBeginTag(HtmlTextWriterTag.Ul);//<ul>

                                    foreach (Category child2 in childCategoryL3)
                                    {
                                        string[] columnChild3 = new string[] { child2.Category_Name, child2.Category_NameBM, child2.Category_NameCH };
                                        wt.RenderBeginTag(HtmlTextWriterTag.Li);//<li>
                                        wt.AddAttribute(HtmlTextWriterAttribute.Href, "#");
                                        wt.RenderBeginTag(HtmlTextWriterTag.A);//<a>
                                        wt.Write(columnChild3[i]);
                                        wt.RenderEndTag();//</a>
                                        wt.RenderEndTag();//</li>
                                    }
                                    wt.RenderEndTag();//</ul>
                                }
                                wt.RenderEndTag();//</li>
                            }

                            wt.RenderEndTag();//</ul>
                        }
                        wt.RenderEndTag();//</li>
                    }

                    wt.RenderEndTag();//</ul>
                    wt.RenderEndTag();//</li>
                }
            }


            string menuHTML = sWriter.ToString();

            string filePath = Path.Combine(strPath, @"Views\Shared\CacheData\CateMenu\");
            new FileInfo(filePath).Directory.Create(); //create new folder
            var menuPath = String.Format("{0}{1}", filePath, tempCateHTML[i]); //create multiple HTML files for multiple language

            using (FileStream fs = new FileStream(menuPath, FileMode.Append, FileAccess.Write))
            {
                StreamWriter sw = new StreamWriter(fs);
                sw.WriteLine(menuHTML);
                sw.Flush();
                sw.Close();
                fs.Close();
            }

            if (!File.Exists(filePath + cateHTML[i]))
            {
                using (File.Create(filePath + cateHTML[i]))
                {
                    //create dummy file if the file doesnt exists
                }
            }

            File.Replace(menuPath, filePath + cateHTML[i], filePath + cateHTML[i] + ".bac");
        }
    }

}

it's a long process. So really Thank you for the time