Check to see if a node is part of a binary search tree

node.rb

class Node
  attr_accessor :left, :right, :value
  
  def is_bst?(min = -1.0/0, max = 1.0/0)
    # exit if the siblings are not of the Node type or Nil and have valid value
    return false unless is_valid?
    
    return false unless left.nil? or left.is_bst?(min, value)
    return false unless right.nil? or right.is_bst?(value, max)
    value > min and value < max
  end
  
  def is_valid?
    # check that the left sibling is nil or of Node type and has a valid value
    return false unless (left.nil? or (left.class == Node and (left.value.class == Fixnum or left.value.class == Float)))
    
    # check that the right sibling is nil or of Node type and has a valid value
    return false unless (right.nil? or (right.class == Node and (right.value.class == Fixnum or right.value.class == Float)))
    
    # check that this node has a valid value
    (value.class == Fixnum or value.class == Float)
  end
end