It shall be unlawful for any person or firm to engage in the business or occupation of pruning, treating or removing street or park trees within the city without first applying for and procuring a license. The license fee shall be $25 annually in advance; provided, however, that, no license shall be required of any public utility company, or its agents, or city employee doing the work in the pursuit of their public service endeavors. Before any license shall be issued, each applicant shall first file evidence of possession of liability insurance in the minimum amounts of $50,000 for bodily injury and $100,000 property damage, indemnifying the city or any person injured, or damage resulting from the pursuit of such endeavors as herein described.