using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public static void Main()

    {        

        var input = "AX,TR,AR,XC,ZC,MM,XM,XB,XT,BV,ZV,XR,DP,DR,DT,DX,RD,RR,RT,RX,RK,IF,XZ,KL,KX,CJ,KT,KZ,DX,DZ,HD,VN,GL,ZL,GG,MX,MZ,MH,HR,XH,ZH,NT,AS,AZ,PH,PX,KS,VX,SM,KV,SB,OT,SZ,SV,XV,TM,TZ,DD,GZ,ZS,MS,TC,VS,SX";

        var part = input.Split(',').GroupBy(x=> x[0]).Select(g=> new {Key=g.Key, Variations= g.Select(x=>x[1]).OrderBy(x=>x)} );

        var sub = part.OrderBy(x=> x.Key).Select(x => $"{x.Key}[{string.Join("", x.Variations)}]");

        var final = String.Join("|",sub);

        Console.WriteLine(final);

    }

}

​