Nokogiri Happymapper - Assignment of Parent Element

tree.rb

require 'happymapper'

class Branch
 include HappyMapper

 attr_accessor :tree
end

class Tree
  include HappyMapper

  has_many :branches, Branch

  def branches
    @branches.each { |branch| branch.tree = self }
  end
end

tree_xml = %{
  <tree>
    <branch name="1"></branch>
    <branch name="2"></branch>
    <branch name="3"></branch>
  </tree>
}

tree = Tree.parse(tree_xml,single: true)
puts tree.branches
puts tree.branches.first.tree