I claim the ornamental design for a treatment head, as shown and described.
FIG. 1 is a perspective view of a treatment head showing my new design;
FIG. 2 is a perspective view of the treatment head of FIG. 1.
FIG. 3 is a top view of the treatment head of FIG. 1.
FIG. 4 is a left-side view of the treatment head of FIG. 1.
FIG. 5 is a front view of the treatment head of FIG. 1.
FIG. 6 is a cross-section view of the treatment head taken along the line 6-6 of FIG. 5; and,
FIG. 7 is a cross-section view taken along the line 7-7 of FIG. 5.
The bottom view is a mirror image of the top view of FIG. 3 and is not illustrated. The right-side view is a mirror image of the left-side view of the treatment head of FIG. 4 and is not illustrated.
The broken lines in the drawings show environmental structure and form no part of the claimed design.