c#字符串按照1.1,1.1.1,2.1,2.1.1排序

 List<string> list = new List<string> { "1", "1.1", "1.1.1", "1.1.2", "1.1.3", "1.2", "1.3", "2", "2.1", "2.2", "2.3", "2.3", "1" };
            list.Sort((x, y) =>
                {
                    int ret = 0;
                    var xsplit = x.Split(".".ToCharArray()).Select(z => int.Parse(z)).ToList();
                    var ysplit = y.Split(".".ToCharArray()).Select(z => int.Parse(z)).ToList();
                    for (int i = 0; i < Math.Max(xsplit.Count, ysplit.Count); i++)
                    {

                        if (xsplit.Count - 1 < i)
                        {
                            ret = -1;
                            return ret;
                        }
                        else if (ysplit.Count - 1 < i)
                        {
                            ret = 1;
                            return ret;
                        }
                        else
                        {
                            ret = xsplit[i] - ysplit[i];
                            if (ret != 0)
                                return ret;
                        }
                    }
                    return  ret;

                });
        }