Amazon put a page up to buy entire April series as a collection. This was something I was thinking of doing but they beat me to it and probably did a better job. I like that it shows if you already bought a book so you don’t irritate people by duplication.
Follow-up. Response from Amazon:
We are glad to hear that you liked our new feature which is called ‘Series Bundle’ that is displaying all the books under the series titled “April.”
However, I’ll have to be honest with you that this is still in testing phase and therefore we have provided this feature only to a certain set of publishers.
Having said that, the additional feature where one can buy all the books in a bundle has not yet been added to your books and which is why your reader has to buy each book individually.
Therefore, I’ve went ahead and introduced this feature to your series bundle so that customers can buy all 6 of your books with just one click. Please note that it may take up to 24 hours for this to update on our website.