The Trejo pistols were made by a small family company in Puebla, Mexico from the late 1940s until the early 1970s. They made primarily .22 LR rimfire pistols, in both small (Model 1) and large (Model 2) frame sizes. They were basically styled after the Colt 1911, but with a more aggressive grip angle.

What makes the Trejos notable is that Mexican law allowed ownership of fully automatic rimfire firearms at that time, and so a subset of the Models 1 and 2 pistols were offered with a select fire switch. This doesn't really have any practical use, given the 8-round magazine of the Model 1 (11 rounds for the larger Model 2) and the roughly 1200-round-per-minute rate of fire...but it does make for a fun recreational machine gun.

Registered fully automatic Trejos like this one are actually quite rare - I suspect because prior to 1968 when they were legal to import, most buyers probably just didn't bother to register them. The NFA was less strenuously enforced back then, and the $200 tax would have been more than the guns cost.