[Update May 2023]
We have added book series as a concept to the backend and we are working to show it on the frontend later this year. Once we get that in place we will really improve this part.
Currently, our platform is limited to choosing 1 book for each of the 5 recommendation spots.
So you can recommend a series, but we would only be able to feature the first book in the series next to that. Of course, you can talk about the entire series (readers prefer starting with book #1, so it isn't a big issue). Feel free to email firstname.lastname@example.org, and we can take a look if you have a unique situation.
I am looking at adding book series data in 2023, but it is a big and expensive project.
P.S. Would you like to help us build features like this faster?
I launched a membership program for founding members at the urging of authors and readers. 100% of the money goes toward developing new features and my goal of hiring a full-time developer in 2023 (currently, we only have one part-time developer).