A level can be defined as virtual or regular level.
Virtual levels allow you to register members to all the levels specified inside the bundle )under ” Bundle Content”, but without being registered to the virtual level itself.
If you specified a level as “virtual” and not a regular level, please make sure your virtual level is indeed defined as virtual inside the Wishlist Bundles settings > Settings tab > Virtual Level is set to “Yes” as seen in the below screenshot:
