The ornamental design for a mapletreelamp, as shown and described.
FIG. 1 is a perspective view of a maple tree lamp.
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left view thereof;
FIG. 5 is a right view thereof;
FIG. 6 is a top view thereof;
FIG. 7 is a bottom view thereof; and,
FIG. 8 is another perspective view thereof when in usage.
The dashed or broken lines shown in the drawings depict portions of the maple tree lamp in which the design is embodied that form no part of the claimed design.