lib/parse/model/associations/collection_proxy.rb
def <<(*list)
        if list.count > 0
          notify_will_change!
          list.flatten.each { |e| collection.push(e) }
        end
      end
def <<(*list)
        if list.count > 0
          notify_will_change!
          list.flatten.each { |e| collection.push(e) }
        end
      end
Append items to the collection