The ornamental design for a treestand, as shown and described.
FIG. 1 is a perspective of a tree stand;
FIG. 2 is a front elevation of the tree stand;
FIG. 3 is a rear elevation of the tree stand;
FIG. 4 is a left side elevation of the tree stand;
FIG. 5 is a right side elevation of the tree stand;
FIG. 6 is a top plan of the tree stand;
FIG. 7 is a top plan of a platform portion of the tree stand as viewed from a line designated 7-7 in FIG. 2;
FIG. 8 is a bottom plan of the tree stand; and,
FIG. 9 is a bottom plan of a seat portion of the tree stand as viewed from a line designated 9-9 in FIG. 3.
The broken lines shown in the figures are for the purposes of illustrating environmental structures and portions of the tree stand; the broken lines form no part of the claimed design.