The ornamental design for a levitating christmastree, as shown and described.
FIG. 1 is a perspective view of a levitating Christmas tree showing my new design in a used condition illustrating a bracket that shows the position of a tree levitating above a base;
FIG. 2 is a rear view thereof;
FIG. 3 is a right side view thereof;
FIG. 4 is a front view thereof;
FIG. 5 is left side elevation thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The broken lines showing a tree including a trunk, branches, oval tips on each branch, the small rectangles within the oval shapes on the ribbon, and the circles on the square bottom stand represent portions of the levitating Christmas tree that form no part of the claimed design.