The ornamental design for a bicycletrailer, as shown and described.
FIG. 1 is a top perspective view of a bicycle trailer;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a right side view thereof;
FIG. 5 is a left side view thereof
FIG. 6 is a top view thereof; and,
FIG. 7 is a bottom view thereof.
The broken lines shown illustrate portions of the bicycle trailer that form no part of the claimed design. All sides not shown form no part of the claimed design.