Man pages matching name btree in section 3:

btree.3.en	debian 10 / manpages-dev
btree.3.es	debian 10 / manpages-es
btree.3.ja	debian 10 / manpages-ja-dev
btree.3.pl	debian 10 / manpages-pl-dev
btree.3.pt	debian 10 / manpages-pt-dev
btree.3.en	debian 11 / manpages-dev
btree.3.es	debian 11 / manpages-es-dev
btree.3.fr	debian 11 / manpages-fr-dev
btree.3.ja	debian 11 / manpages-ja-dev
btree.3.pl	debian 11 / manpages-pl-dev
btree.3.pt	debian 11 / manpages-pt-dev
btree.3.en	debian 12 / manpages-dev
btree.3.es	debian 12 / manpages-es-dev
btree.3.fr	debian 12 / manpages-fr-dev
btree.3.ja	debian 12 / manpages-ja-dev
btree.3.pl	debian 12 / manpages-pl-dev
btree.3.ru	debian 12 / manpages-ru-dev