I claim the ornamental design for a trek saw, as shown and described.
FIG. 1 is a front, side perspective view of a trek saw, showing my new design;
FIG. 2 is a front-side elevational view thereof;
FIG. 3 is a back-side elevational view thereof;
FIG. 4 is a left-side elevational view thereof, the trek saw having generally a rotational axis of symmetry such that the left-side and the right side views are mirror images;
FIG. 5 a top plan view thereof; and,
FIG. 6 is a bottom plan view thereof.
The broken lines depict portions of the trek saw in which the design is embodied that are not considered part of the claimed design.