The ornamental design for a christmastreetopperbow, as shown and described.
FIG 1 is a perspective view of a Christmas tree topper bow, showing my new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a right side view thereof;
FIG. 5 is a left side view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The broken lines shown in the drawings represent portions of the Christmas tree in FIG. 1 that form no part of the claimed design. The surface shading illustrated in the drawings is provided merely to highlight the contour of the design; it is not intended to be illustrative of texture or gloss.