The ornamental design of a christmastreeornament, as shown and described.
FIG. 1 is a front view, with the top tilted slightly backward, of my
design, the design having ten points and being approximately symmetrical
about three vertical planes;
FIG. 2 is a side view of my design, with the ornament rotated approximately
60° about its vertical axis from the position shown in FIG. 1;