private List<PermissionModel> GetMenu(List<PermissionModel> list, long pid)
        {
            Func<long, List<PermissionModel>> func = null;
            func = new Func<long, List<PermissionModel>>(m =>
            {
                List<PermissionModel> t = new List<PermissionModel>();
                foreach (var item in list.Where(h => h.ParentId == m))
                {
                    var childs = func(item.Id);
                    PermissionModel model = new PermissionModel();
                    model.Id = item.Id;
                    model.Url = item.Url;
                    model.Icon = item.Icon;
                    model.Title = item.Title;
                    model.Param = item.Param;
                    model.ParentId = item.ParentId;
                    model.PermissionType = item.PermissionType;
                    model.Sort = item.Sort;
                    model.Children = childs.OrderBy(i => i.Sort).ToList();
                    t.Add(model);
                }
                t = t.OrderBy(i => i.Sort).ToList();
                return t;
            });
            return func(pid);
        }

解释：初次调用传入参数：list,pid。
list:从数据库中查出的菜单集合
pid:一级菜单的父ID,比如：0