tree.rb

class Node
  include Enumerable

  attr_accessor :left, :right, :data

  def initialize(data)
    @data = data
    @left = nil
    @right = nil
  end

  def each(&block)
    left.each(&block) if left
    block.call(self)
    right.each(&block) if right
  end

  def <=>(other)
    @data <=> other.data
  end

  def <=(other)
    @data <= other.data
  end

  def >=(other)
    @data >= other.data
  end
end

class Tree
  attr_accessor :root

  def initialize(root)
    @root = root
  end

  def insert(node)
    insert_p(node, @root)
  end

  private
  def insert_p(node, root)
    if node <= root
      if root.left.nil?
        root.left = node
      else
        insert_p(node, root.left)
      end
    elsif node >= root
      if root.right.nil?
        root.right = node
      else
        insert_p(node, root.right)
      end
    end
  end
end

a = Node.new(3)
b = Node.new(4)
c = Node.new(5)

t = Tree.new(a)
t.insert(b)
t.insert(c)
t.insert(Node.new(1))

p t