I claim the ornamental design for a tree stand platform, as shown and described.
FIG. 1 is a perspective view of a tree stand platform;
FIG. 2 is a top view thereof;
FIG. 3 is a left side view thereof, the right side view being a mirror image of the left side view shown;
FIG. 4 is a front view thereof; and,
FIG. 5 is a rear view thereof.
The ornamental design which is claimed is shown in solid lines in the drawings. The broken lines in the drawings are for illustrative purposes only and form no part of the claimed design.