using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var tree = new Tree {

            Children = new List<Tree> {

                new Tree(),

                new Tree(),

                new Tree {

                    Children = new List<Tree> {

                        new Tree()

                    }

                }

            }

        };

        Action<Tree> f = (Tree t) => Console.WriteLine(t.Name);

        Dfs(f, tree);

    }

    public static void Dfs(Action<Tree> f, Tree root) {

        f(root);

        foreach(var child in root.Children)

            Dfs(f, child);

    } 

    public class Tree {

        public Guid Name {get;set;}

        public IEnumerable<Tree> Children {get;set;}    

        public Tree() 

        {

            Name = Guid.NewGuid();

            Children = new List<Tree>();

        }

    }

}