Tree with compare function, the insertion is quite complex but i just wanted it to work.

mirror_check.rb

require './Tree'

include Tree

root = Node.new(1)

root.insert(Node.new(2), -1).insert(Node.new(3), -1).insert(Node.new(3), -1)
root.insert(Node.new(2), 1).insert(Node.new(3), 1).insert(Node.new(3), 1)

root.each do |node|
  puts "#{node.word} * "
end

if root.compare_node
	puts "Mirror image"
else
	puts "Not a Mirror image"
end

Tree.rb

module Tree
  class Node
    attr_reader :word, :left, :right
    include Enumerable
    def initialize(value)
      @word = value
      @left = @right = nil
    end

    def insert(node, dir)
      if dir < 0
        @left = node
        return @left
      else
        @right = node
        return @right
      end
    end

    def each
      @left.each {|node| yield node } unless @left.nil?
      yield self
      @right.each {|node| yield node } unless @right.nil?
    end

    def compare_node()
      return compare(@left, @right)
    end

    # compare two nodes n1 and n2: recursive function which checks if the value is same
    # if it is same it continues to compare (1.left and 2.right) and (1.right and 2.left)
    def compare(n1, n2)
      if n1.nil? && n2.nil?
        return true
      elsif !n1.nil? && !n2.nil?
        if(n1.word == n2.word)
          return compare(n1.left, n2.right) && compare(n1.right, n2.left)
        else
          return false
        end
      else
        return false
      end
    end
  end
end