Is InnoDB Engine a B Tree or a B+ Tree?

I am confused about the InnoDB Engine. In the original document, it states that InnoDB uses a B Tree. However, in some other articles, they claim that InnoDB uses a B+ Tree. - https://dev.mysql.com/doc/refman/8.3/en/innodb-physical-structure.html - https://blog.jcole.us/2013/01/10/btree-index-structures-in-innodb/ - https://iorilan.medium.com/why-does-innodb-engine-use-the-b-tree-data-structure-for-indexing-6c4a41f6f356 Can you help me understand my confusion? I'm not sure whether the InnoDB Engine is a B Tree or a B+ Tree. I apologize if I've misunderstood it.