simple_validator.rb

class BulkPeriodValidator(array_of_periods)
  @array_of_periods = array_of_periods

  def valid?
    values = value.map { |elem| [elem.endless, elem.trial] }
    values.size == values.uniq.size
  end
end

period_validator = BulkPeriodValidator.new(your_array_of_periods)
period_validator.valid?