The ornamental design for a bicycletrailer, as shown and described.
FIG. 1 is a perspective view of the bicycle trailer showing my new design;
FIG. 2 is a left side elevation view thereof;
FIG. 3 is a front side view elevation view thereof;
FIG. 4 is a back side elevation view thereof; and,
FIG. 5 is a top side elevation view thereof.
The portions of the drawings shown in broken lines show attachment parts of the bicycle trailer such as wheels, chassis components, handle, and draw bar. The broken line illustrations form no part of the claimed design.