The ornamental design for a christmastreewatering funnel with flexible tube, as shown and described.
FIG. 1 is a front perspective view of a Christmas tree watering funnel with flexible tube showing my new design;
FIG. 2 is a side view (opposite side view is mirror image) thereof;
FIG. 3 is a top view thereof;
FIG. 4 is a bottom view thereof; and,
FIG. 5 is an environmental perspective view of the Christmas tree watering tube in use.
In FIG. 5, the broken lines showing of environmental structure for purposes of illustrating the Christmas tree watering funnel with flexible tube. The broken lines and the structure they depict form no part of the claimed design.