The ornamental design for a risingplatform, as shown and described.
FIG. 1 is a perspective view of a rising platform having a top surface according to a first embodiment of our new design in a first position;
FIG. 2 is a perspective view of the rising platform according to the first embodiment in a second position which is raised and rotated relative to the first position;
FIG. 3 is top plan view of FIG. 2;
FIG. 4 is one side view of FIG. 3; and,
FIG. 5 is a second side view taken 180 degrees from FIG. 4.
The dash-dash broken lines illustrate environmental structure and form no part of the claimed design.