The ornamental design for a tricycle, as shown and described.
FIG. 1 is a perspective view of a tricycle;
FIG. 2 is a right-side view of the tricycle of FIG. 1;
FIG. 3 is a rear view of the tricycle of FIG. 1;
FIG. 4 is a front view of the tricycle of FIG. 1;
FIG. 5 is top plan view of the tricycle of FIG. 1; and,
FIG. 6 is a bottom plan view of the tricycle of FIG. 1.
The left-side view of the tricycle of FIG. 1 is a mirror image of the right-side view of FIG. 2. The broken lines showing the remainder of a tricycle form no part of the claimed design.