FIG. 1 is a perspective view of a branch lamp showing my new design; FIG. 2 is a front elevational view thereof; FIG. 3 is a rear elevational view thereof; FIG. 4 is a right side elevational view thereof; FIG. 5 is a left side elevational view thereof; FIG. 6 is a top view thereof; and, FIG. 7 is a bottom view thereof. Broken lines in figures are for illustrative purposes only and form no part of the design.