using System;

using System.Collections.Generic;

public class Program

{

    private class ToOrder { 

        public Guid? ParentId { get; set; }

        public Guid Id { get; set; }

    }

    public static void Main()

    {

​

        var id1 = Guid.NewGuid();

        var id2 = Guid.NewGuid();

        var id3 = Guid.NewGuid();

        var guids = new List<ToOrder>();

guids.Add(new ToOrder() { ParentId = Guid.Parse("033e0cff-80b7-4173-b323-3c23b4168ba7"), Id = Guid.Parse("cbcb97a7-a5df-4f4b-9c5e-022e596821ae") });

guids.Add(new ToOrder() { ParentId = Guid.Parse("033e0cff-80b7-4173-b323-3c23b4168ba7"), Id = Guid.Parse("181ebc8c-f6be-437c-a14e-05c56a935819") });

guids.Add(new ToOrder() { ParentId = Guid.Parse("181ebc8c-f6be-437c-a14e-05c56a935819"), Id = Guid.Parse("3d518868-5400-48a6-b186-1079a694af38") });

guids.Add(new ToOrder() { ParentId = Guid.Parse("9fc70791-b3db-4cb1-9c35-fd10a4fbaafb"), Id = Guid.Parse("0806074c-2de8-47b0-8347-198e97e573f9") });

guids.Add(new ToOrder() { ParentId = Guid.Parse("b04593b0-8f22-4d31-9e30-e53df9860ccb"), Id = Guid.Parse("083ceba1-3d04-4154-8c66-1c4d31411d18") });

guids.Add(new ToOrder() { ParentId = Guid.Parse("033e0cff-80b7-4173-b323-3c23b4168ba7"), Id = Guid.Parse("e78b1ae1-cb21-4694-bd9a-2e74c1c09d86") });

guids.Add(new ToOrder() { ParentId = Guid.Parse("3d518868-5400-48a6-b186-1079a694af38"), Id = Guid.Parse("9f322f75-45e6-4d3a-be17-37de3bdc22bb") });

guids.Add(new ToOrder() { ParentId = Guid.Parse("3d518868-5400-48a6-b186-1079a694af38"), Id = Guid.Parse("73cf99c0-b960-4340-ac56-3ab6dd17be2c") });

guids.Add(new ToOrder() { ParentId = null,  Id = Guid.Parse("033e0cff-80b7-4173-b323-3c23b4168ba7")});

guids.Add(new ToOrder() { ParentId = Guid.Parse("033e0cff-80b7-4173-b323-3c23b4168ba7"),    Id = Guid.Parse("e792bfb4-11be-4633-8f9d-50194fa7045c") });

guids.Add(new ToOrder() { ParentId = Guid.Parse("73cf99c0-b960-4340-ac56-3ab6dd17be2c"),    Id = Guid.Parse("26aa43fd-56ba-4dc6-8a1b-5130cc2c8bf2") });

guids.Add(new ToOrder() { ParentId = Guid.Parse("9f322f75-45e6-4d3a-be17-37de3bdc22bb"),    Id = Guid.Parse("440b1ae0-e29c-4959-a7fe-629e0a2fdf85") });

guids.Add(new ToOrder() { ParentId = Guid.Parse("73cf99c0-b960-4340-ac56-3ab6dd17be2c"),    Id = Guid.Parse("20ea8c08-a1c9-416a-93cd-8065a0e59684") });

guids.Add(new ToOrder() { ParentId = Guid.Parse("9f322f75-45e6-4d3a-be17-37de3bdc22bb"),    Id = Guid.Parse("fa2cacaf-fa09-48e0-bbda-8634ba0ee0eb") });

guids.Add(new ToOrder() { ParentId = Guid.Parse("b04593b0-8f22-4d31-9e30-e53df9860ccb"),    Id = Guid.Parse("10bc7268-ca13-4ca9-8465-a13355be5b30") });

guids.Add(new ToOrder() { ParentId = Guid.Parse("9fc70791-b3db-4cb1-9c35-fd10a4fbaafb"),    Id = Guid.Parse("1369b880-c1fc-4dcd-892b-cef49da3b0ba") });

guids.Add(new ToOrder() { ParentId = Guid.Parse("fa82ace2-0dba-40c4-b62c-e8ac99397bd7"),    Id = Guid.Parse("5c49c08a-a6a5-41f3-8fcf-d8f91c3738bf") });

guids.Add(new ToOrder() { ParentId = Guid.Parse("e792bfb4-11be-4633-8f9d-50194fa7045c"),    Id = Guid.Parse("b04593b0-8f22-4d31-9e30-e53df9860ccb") });

guids.Add(new ToOrder() { ParentId = Guid.Parse("3d518868-5400-48a6-b186-1079a694af38"),    Id = Guid.Parse("fa82ace2-0dba-40c4-b62c-e8ac99397bd7") });

guids.Add(new ToOrder() { ParentId = Guid.Parse("9fc70791-b3db-4cb1-9c35-fd10a4fbaafb"),    Id = Guid.Parse("f69930ef-eb69-4b0a-8b30-e9906d21f4d9") });

guids.Add(new ToOrder() { ParentId = Guid.Parse("f69930ef-eb69-4b0a-8b30-e9906d21f4d9"),    Id = Guid.Parse("1a72017b-7daf-46fb-8c6f-f47cfff4fe1d") });

guids.Add(new ToOrder() { ParentId = Guid.Parse("fa82ace2-0dba-40c4-b62c-e8ac99397bd7"),    Id = Guid.Parse("bd600a75-c53e-4961-aec4-f817a54c2e20") });

guids.Add(new ToOrder() { ParentId = Guid.Parse("3d518868-5400-48a6-b186-1079a694af38"),    Id = Guid.Parse("9fc70791-b3db-4cb1-9c35-fd10a4fbaafb") });

​

​

        guids.Sort((org1, org2) => org1.ParentId == org2.Id ? 1 : -1);

        foreach(var x in guids) {

            Console.WriteLine((x.ParentId ?? Guid.Empty) + " " +  x.Id);

        }

    }

}