using System;

using System.Linq;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        var items = GetItems();

        var resultingStrings =

            from parent in items.Where(x => x.ParentId == 0)join child in items on parent.Id equals child.ParentId

            join grandChild in items on child.Id equals grandChild.ParentId

            select string.Format("{0}:{1}:{2}", parent.Name, child.Name, grandChild.Name);

        foreach (var item in resultingStrings)

            Console.WriteLine(item);

    }

​

    public static List<Item> GetItems()

    {

        var list = new List<Item>();

        list.Add(new Item{Id = 1, Name = "Parent1", ParentId = 0});

        list.Add(new Item{Id = 2, Name = "Child1", ParentId = 1});

        list.Add(new Item{Id = 3, Name = "Child2", ParentId = 1});

        list.Add(new Item{Id = 4, Name = "GrandChild1", ParentId = 2});

        list.Add(new Item{Id = 5, Name = "GrandChild2", ParentId = 2});

        list.Add(new Item{Id = 6, Name = "GrandChild3", ParentId = 3});

        list.Add(new Item{Id = 7, Name = "GrandChild4", ParentId = 3});

        list.Add(new Item{Id = 8, Name = "Parent2", ParentId = 0});

        list.Add(new Item{Id = 9, Name = "Child1", ParentId = 8});

        list.Add(new Item{Id = 10, Name = "Child2", ParentId = 8});

        list.Add(new Item{Id = 11, Name = "GrandChild1", ParentId = 9});

        list.Add(new Item{Id = 12, Name = "GrandChild2", ParentId = 9});

        list.Add(new Item{Id = 13, Name = "GrandChild3", ParentId = 10});

        list.Add(new Item{Id = 14, Name = "GrandChild4", ParentId = 10});

        return list;

    }

}

​

public class Item

{

    public int Id

    {

        get;

        set;

    }

​

    public string Name

    {

        get;

        set;

    }

​

    public int ParentId

    {

        get;

        set;

    }

}