All lamp posts and all shade or ornamental trees, hereafter placed in any of the streets of the City, shall be placed within and not more than one (1) foot from the outer line of the sidewalk of such street; provided that the Director of Public Service may, at his or her discretion, permit the planting of a second row of shade trees on sidewalks of not less than twenty (20) feet in width. The second row of trees shall be at least twelve (12) feet from the line of the street.