using System.Collections.Generic;

using System;

public class Program

{

    public static void Main()

    {

        var tree = new Tree<string>()

            .Begin("Fastfood")

                .Begin("Pizza")

                    .Add("Margherita")

                    .Add("Marinara")

                .End()

                .Begin("Burger")

                    .Add("Cheese burger")

                    .Add("Chili burger")

                    .Add("Rice burger")

                .End()

            .End();

        tree.Nodes.ForEach(p => PrintNode(p, 0));

    }

    static void PrintNode<T>(TreeNode<T> node, int level)

    {

        Console.WriteLine("{0}{1}", new string(' ', level*3), node.Value);

        level++;

        node.Children.ForEach(p => PrintNode(p, level));

    }

}

​

public class TreeNode<T>

{

    public T Value {get;}

    public TreeNode<T> Parent {get;}

    public List<TreeNode<T>> Children {get; }

    public TreeNode(T val, TreeNode<T> parent)

    {

        Value = val;

        Parent = parent;

        Children = new List<TreeNode<T>>();

    }

    public TreeNode<T> Add(T val)

    {

        var node = new TreeNode<T>(val,this);

        Children.Add(node);

        return node;

    }

}

​

​

public class Tree<T>

{

    private Stack<TreeNode<T>> m_Stack = new Stack<TreeNode<T>>();

    public List<TreeNode<T>> Nodes{get;} = new List<TreeNode<T>>();

    public Tree<T> Begin(T val)

    {

        if(m_Stack.Count==0)

        {

            var node = new TreeNode<T>(val, null);

            Nodes.Add(node);

            m_Stack.Push(node);

        }

        else

        {

            var node = m_Stack.Peek().Add(val);

            m_Stack.Push(node);

        }

        return this;

    }

    public Tree<T> Add(T val)

    {

        m_Stack.Peek().Add(val);

        return this;

    }

    public Tree<T> End()

    {

        m_Stack.Pop();

        return this;

    }

}

​

​