For those using the Instant-On function of the console, you might not be seeing your full list of backwards compatible games. In the support forums people are instructed to reboot [restart or power cycle] their console to try to get their full list of games to be refreshed.
If you have digitally purchased a BC X360 game and it doesn't show up in your Xbox One Ready to Install list, you will need to try one more step if you still have your X360 console, boot up the X360 and start playing the game (s) in question.
If that step still doesn't refresh your Xbox One Ready to Install List or you no longer own a X360, then you need to fill out a survey. From that survey, support will be able to troubleshoot the issue.
Direct Link to Survey:
https://twtpoll.com/backwardcompatibility
Verified Post on Troubleshooting X360 BC on Xbox One:
http://forums.xbox.com/xbox_support/xbox_one_support/f/5574/t/2060648.aspx