using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

     public class ProductDTO

     {

         public int Id { get; set; }

         public string Name { get; set; }

         public int? Parent { get; set; }

         public override string ToString() {

             return "[" + Id + " - " + Name + "]";

         }

         public int Deep { get; set; }

     }

    public static void Main()

    {

        Console.WriteLine("Hello World");

​

         var products = new List<ProductDTO>();

         products.Add(new ProductDTO() { Id = 7, Name = "Child One", Parent = 3 });

         products.Add(new ProductDTO() { Id = 10, Name = "Child One", Parent = 4 });

         products.Add(new ProductDTO() { Id = 8, Name = "Child Three", Parent = 1 });

         products.Add(new ProductDTO() { Id = 9, Name = "Child Two", Parent = 2 });

         products.Add(new ProductDTO() { Id = 1, Name = "Product One" });

         products.Add(new ProductDTO() { Id = 2, Name = "Product Two" });

         products.Add(new ProductDTO() { Id = 6, Name = "Child Two", Parent = 1 });

         products.Add(new ProductDTO() { Id = 4, Name = "Child One", Parent = 1 });

         products.Add(new ProductDTO() { Id = 5, Name = "Child One", Parent = 2 });

         products.Add(new ProductDTO() { Id = 3, Name = "Product Three" });

        var ordered = GetOrderedList(products, null, 0);

        foreach(var item in ordered) {

            for(int i = 0; i < item.Deep; i++) {

                Console.Write("\t");

            }

            Console.Write(item.ToString());

            Console.Write("\n");

        }

    }

    public static List<ProductDTO> GetOrderedList(List<ProductDTO> Items, int? root, int deep) {

        var result = new List<ProductDTO>();

        foreach(var item in Items.Where(x => x.Parent == root).OrderBy(x => x.Id)) {

            item.Deep = deep;

            result.Add(item);

            result.AddRange(GetOrderedList(Items, item.Id, deep + 1));

        }

        return result;

    }

}