Ruby помогите с синтаксисом

class Tree
attr_accessor :left
  attr_accessor :right
  attr_accessor :data

  def initialize(x=nil)
   @left = nil
   @right = nil
   @data = x
  end
   def insert(x)
    if @data == nil
     @data = x
    elsif x <= @data
     if @left == nil
      @left = Tree.new x
     else
      @left.insert x
     end
    else
     if @right == nil
      @right = Tree.new x
     else
      @right.insert x
     end
    end
   end

   def inorder()
    @left.inorder {|y| yield y} if @left != nil
    yield @data
    @right.inorder {|y| yield y} if @right != nil
   end

 def traverse()
   list = []
   yield @data
   list << @left if @left != nil
   list << @right if @right != nil
   loop do
    break if list.empty?
    node = list.shift
    yield node.data
    list << node.left if node.left != nil
    list << node.right if node.right != nil
   end
  end
  end
  items = [50, 20, 80, 10, 30, 70, 90, 5, 14,
       28, 41, 66, 75, 88, 96]

  tree = Tree.new

  items.each {|x| tree.insert(x)}

  tree.inorder {|x| print x, " "}
  print "\n"