CategoryTree - information
Fragment of a discussion from Project:Support desk
You can change it by editing the page MediaWiki:categorytree-member-num in your wiki (for example on this wiki it is set to "($1 C, $2 P, $3 F)") which means category tree should output a bracket followed by number of categories ($1), followed by the letter C, and so on.
I can't really think of a better way to put it than whats currently on the extension page
