Treenode problem

treenode.rb

class TreeNode
  attr :children
  attr_reader :parent
 
  def name=(value)
    @name=value
  end
  
  def name
    @name
  end
  
  def parents
    @parents
  end
  
  def parents=(value)
    @parents=value
  end

  def initialize(name=nil)
    @name = name
    @children = []
    @parents = []
  end

  def add_child(child)
    @children << child
    child.parent = self
    child.parents = self.parents
    child.add_parent(self)
  end

  def add_parent(parent)
    @parents << parent
  end
  
  def parent_count
    @parent.count
  end
  
  def children_count
    @children.count
  end

  def parent=(new_parent)
    @parent = new_parent
  end
  
  def is_child?(tree_node)
    if tree_node.parent == self
      true
    else
      false
    end
  end
  
  def show_ancestors
    self.parents.each do |parent|
      print "#{parent.name}"
      print ">"
    end
    print self.name
  end

end

node_parent = TreeNode.new("parent")
node_child = TreeNode.new("child")
node_grandchild = TreeNode.new("grandchild")

node_parent.add_child(node_child)
node_child.add_child(node_grandchild)

node_grandchild.show_ancestors