Pupli

public JsonResult GetCategories()
        {
            nDownloadEntities entities = new nDownloadEntities();
            List<Category> categories = entities.Categories.ToList();

            var sb = new StringBuilder();

            var roots = GetRoots(categories);
            string unorderedList = GenerateUL(roots, categories, sb);

            return Json(unorderedList, JsonRequestBehavior.AllowGet);
        }

        [NonAction]
        private List<Category> GetRoots(List<Category> categories)
        {
            var roots = categories.Where(x => x.ParentId == 0).ToList();
            return roots;
        }

        [NonAction]
        private string GenerateUL(List<Category> parents, List<Category> categories, StringBuilder sb)
        {
            sb.AppendLine("<ul>");

            if (parents.Count > 0)
            {
                foreach (Category category in parents)
                {
                    string line = String.Format(@"<li>{0}", category.CategoryText);
                    sb.Append(line);

                    List<Category> subMenu=categories.Where(x=>x.ParentId==category.CategoryId).ToList();
                    if (subMenu.Any())
                    {
                        var subMenuBuilder = new StringBuilder();
                        sb.Append(GenerateUL(subMenu, categories, subMenuBuilder));
                    }
                    sb.Append("</li>");
                }
            }

            sb.Append("</ul>");
            return sb.ToString();
        }

References :
http://stackoverflow.com/questions/14137811/generate-nested-menu-from-datatable-using-c-sharp-as-ul-list-not-asp-net-menu-co

Keywords :

ul , li , treeview , menu , recursive