The ornamental design for an artificial christmastree, as shown and described.
1. Artificial Christmas tree
1.1 is a front view of an artificial Christmas tree showing my new design;
1.2 is a back view thereof;
1.3 is a side view thereof;
1.4 is an opposite side view thereof;
1.5 is a top view thereof; and
1.6 is a perspective view thereof.
The present artificial Christmas tree design consists of a pedestal, a trunk, horizontal branches and a star on the top of the trunk; branches of different sizes are positioned through holes in the trunk successively from the shortest at the top to the longest at the bottom.