Description of problem:
Original two button Microsoft PS/2 mouse autodetected as a generic tree button
There's no way to differentiate between a two and a three button mouse by probing.
I have to agree after reading other sources.
Please be on the safe side and assume these kind of mice as 2 button or at least
select emulate 3 button by default.
Well 3 buttons mice have been the norm for ages so thats why we assume 3 button.
I realize that doesn't work for everyone but I think it works for the vast majority.