## Backend code...

class Node
  attr_reader :title, :parent

  def initialize(title, parent=nil)
    @title = title
    @parent = parent
  end
end

class NodeSet

  class Mapper
    def initialize(set)
      @set = set
    end

    def add(*entities, &block)
      options = entities.extract_options!

      entities.each { |entity| yield map_node(entity, options.dup) }
    end

    private
    def map_node(entities, options)
      @set.add_node(entities, options.to_s)
    end
  end

  attr_accessor :nodes

  def initialize
    self.nodes = Array.new
  end

  def draw
    yield Mapper.new(self)
  end

  def add_node(title, parent=nil)
    nodes << node = Node.new(title, parent)
    node
  end

  def empty?
    nodes.empty?
  end
end

module NodeService
  module Backend
    Nodes = NodeSet.new
  end
end

## testing

NodeService::Backend::Nodes.inspect

## Result

#<NodeSet:0xb700b650 @nodes=[#<Node:0xb700b420 @parent="testtesting", @title="Root">, #<Node:0xb700b380 @parent="", @title="Hej">]>