Very interesting information.
See if I'm right, so for performance purposes, would it be better to consider the columns: fast_root and fast_level instead of the root and level columns?
I have read that even deleting records the B-tree tree is not rebuilt, so it does not cause overhead in dbms, and can have null pointers.
In my example, the values of fast_root, fast_root are equal to root, level, I believe that due to the newly created index and no delete operations occurred in the table.
Best Regards
Neto