static void Main(string[] args)
        {
            List<BankAccountFile> fileList = new List<BankAccountFile>
            {
                 new BankAccountFile{   BankCode= "ICBC",
        BankAccountNum= "1001222309024",
        Period="202105",
        BankAcctPath="D:\\SEPC.FSSC.ReceiptFile\\ICBC\\DZD\\month\\1001222309024_202105_page1_001.html"
                 },
                  new BankAccountFile{   BankCode= "ICBC",
        BankAccountNum= "1001222309024",
        Period="202105",
        BankAcctPath="D:\\SEPC.FSSC.ReceiptFile\\ICBC\\DZD\\month\\1001222309024_202105_page1_002.html"
                 },
                   new BankAccountFile{   BankCode= "ICBC",
        BankAccountNum= "1001222309024",
        Period="202105",
        BankAcctPath="D:\\SEPC.FSSC.ReceiptFile\\ICBC\\DZD\\month\\1001222309024_202105_page1_003.html"
                 },
                    new BankAccountFile{   BankCode= "ICBC",
        BankAccountNum= "1001222309024",
        Period="202105",
        BankAcctPath="D:\\SEPC.FSSC.ReceiptFile\\ICBC\\DZD\\month\\1001222309024_202105_page1_004.html"
                 },
                       new BankAccountFile{   BankCode= "ICBC",
        BankAccountNum= "1001222309024",
        Period="202106",
        BankAcctPath="D:\\SEPC.FSSC.ReceiptFile\\ICBC\\DZD\\month\\1001222309024_202106_page1_001.html"
                 },
                                 new BankAccountFile{   BankCode= "ICBC",
        BankAccountNum= "1001222309024",
        Period="202106",
        BankAcctPath="D:\\SEPC.FSSC.ReceiptFile\\ICBC\\DZD\\month\\1001222309024_202106_page1_002.html"
                 },
                                  new BankAccountFile{   BankCode= "ICBC",
        BankAccountNum= "1001222309024",
        Period="202106",
        BankAcctPath="D:\\SEPC.FSSC.ReceiptFile\\ICBC\\DZD\\month\\1001222309024_202106_page1_002.html"
                 }
             };

            List<BankAccountFile> newList1 = new List<BankAccountFile>(); 
            foreach (IGrouping<string, BankAccountFile> group in fileList.GroupBy(c => c.Period))
            {

                BankAccountFile model = new BankAccountFile();
                model.Period = group.Key; 
                foreach (BankAccountFile stu in group.OrderBy(a => a.Period))
                {
                    Console.Write(stu.BankAcctPath + ";");
                    model.BankCode = stu.BankCode;
                    model.BankAccountNum = stu.BankAccountNum;
                    model.BankAcctPath = stu.BankAcctPath; 
                }
                model.FileList = group.OrderBy(a => a.Period).ToList();
                newList1.Add(model); 
            } 
        }

        public class BankAccountFile
        {
            /// <summary>
            /// 银行简码
            /// </summary>
            public string BankCode { get; set; }
            /// <summary>
            /// 银行账号
            /// </summary>
            public string BankAccountNum { get; set; }
            /// <summary>
            /// 期间
            /// </summary>
            public string Period { get; set; }
            /// <summary>
            /// 下载路径
            /// </summary>
            public string BankAcctPath { get; set; }

            /// <summary>
            /// 银行账号名称
            /// </summary>
            public string BankAccountName { get; set; }

            /// <summary>
            /// 组装多条数据的List
            /// </summary>
            public List<BankAccountFile> FileList { get; set; }
        }