C# 一次循环获取树的两种方法

 private static List<Menu> MenuTree()
        {
            var menu1 = new Menu { Id = 1, ParentId = 0, Name = "aaa" };
            var menu2 = new Menu { Id = 2, ParentId = 0, Name = "bbb" };
            var menu3 = new Menu { Id = 3, ParentId = 0, Name = "ccc" };
            var menu4 = new Menu { Id = 4, ParentId = 1, Name = "ddd" };
            var menu5 = new Menu { Id = 5, ParentId = 2, Name = "eee" };
            var menu6 = new Menu { Id = 6, ParentId = 4, Name = "fff" };
            var menu7 = new Menu { Id = 7, ParentId = 5, Name = "ggg" };
            var menu8 = new Menu { Id = 8, ParentId = 6, Name = "hhh" };
            var menuAll = new List<Menu> { menu1, menu2, menu3, menu4, menu5, menu6, menu7, menu8 };
            var menuList = new List<Menu> { menu1, menu2, menu3, menu4, menu5, menu7, menu8 };
          //第一种方法
            while (true)
            {
                var idList = menuList.Select(x => x.Id).ToList();
                idList.AddRange(menuList.Select(x => x.ParentId).ToList());
                idList = idList.Distinct().ToList();
                var menus = menuAll.Where(x => idList.Contains(x.Id)).ToList();
                if (menus.Count != menuList.Count)
                {
                    menuList = menus;
                    continue;
                }
                break;
            }
　　　　　　　//第二种方法　
            var ret = new List<Menu>();
            foreach (var menu in menuList)
            {
                var model = menuList.FirstOrDefault(x => x.Id == menu.ParentId);
                if (model == null)
                {
                    ret.Add(menu);
                    continue;
                }
                model.Children.Add(menu);
            }
            return ret;
        }