It's not necessary to add an extra 吗 or 呢 after an alternative question in modern Chinese.
你是不是中国人?
You are (or) not are Chinese?
Are youtyou Chinese (or not)?
你吃不吃?
You eat (or) not to eat?
Do you want to eat (or not)?
你去不去?
You go (or) not to go?
Do you want to go (or not)?