using System;

using System.Collections.Generic;

using System.Linq;

namespace ConsoleAppTest

{

    class Program

    {

        static void Main(string[] args)

        {

            var aa = new AA();

            var tree = new Tree() { Id = , Name = "" };

            aa.CreateTree(ref tree);

            Console.WriteLine();

        }

    }

    public class Tree

    {

        public Tree()

        {

            Childrens = new List<Tree>();

        }

        public int Id { get; set; }

        public string Name { get; set; }

        public List<Tree> Childrens { get; set; }

    }

    public class Product

    {

        public int Id { get; set; }

        public string Name { get; set; }

        public int Fid { get; set; }

    }

    public class AA

    {

        List<Product> Products = new List<Product>() {

                new Product(){Id=,Name="",Fid=},

                new Product(){Id=,Name="",Fid=},

                new Product(){Id=,Name="",Fid=},

                new Product(){Id=,Name="",Fid=},

                new Product(){Id=,Name="",Fid=},

                new Product(){Id=,Name="",Fid=},

                new Product(){Id=,Name="",Fid=},

                new Product(){Id=,Name="",Fid=},

            };

        public void CreateTree(ref Tree tree)

        {

            var id = tree.Id;

            var list = Products.Where(x => x.Fid == id).ToList();

            if (list.Any())

            {

                foreach (var item in Products.Where(x => x.Fid == id).ToList())

                {

                    var treeSon = new Tree

                    {

                        Id = item.Id,

                        Name = item.Name

                    };

                    tree.Childrens.Add(treeSon);

                    Console.WriteLine($"{tree.Id}");

                    CreateTree(ref treeSon);

                }

            }

            else

            {

                Console.WriteLine($"{tree.Id}");

            }

        }

    }

}