Sec. 21-6. Poles, Wires And Ropes; Regulations:
   (a)   No person shall attach any wire or rope to any tree or shrub on any public street, parkway or other public place without the permission of the Board of Trustees.
   (b)   Any person which maintains poles and wires in the streets, alleys or other public places, shall, in the absence of provision in the franchise covering the subject, keep such wires and poles free from and away from any trees and shrubs in such places as far as possible, and shall keep all such trees and shrubs near such wires and poles properly trimmed, subject to the supervision of the Director of Public Works, so that no injury shall be done either to the poles or wires or to the shrubs and trees by their contact. (1963 Code § 11.406)