Mysql index use B-tree or B+ tree

Question

I've been told many times that mysql use B+ tree as index data structure, and in this question it also said index story in B+ tree. But I find something different in Mysql official document, in mysql indexes it says Most MySQL indexes (PRIMARY KEY, UNIQUE, INDEX, and FULLTEXT) are stored in B-trees

so I wonder which one is right, B-Tree or B+ tree?

Answer 1

https://dev.mysql.com/doc/internals/en/innodb-fil-header.html

You can look at this sentence in the documentation:

This is a sophistication which you won't find in the classic B-tree, which is why InnoDB should perhaps be called a B+-tree instead