Depends on the municipality and the project. I've done a few projects for pretty small towns - like just 20-30 young trees for young tree training. A couple of those were requiring somebody who has been through the State Division of Forestry's (free) young tree training program.
I've also done some pesticide treatments for a slightly larger town (+-30K, so not big city!). I know the forester from various training events, etc... He calls a couple of companies he knows to be reputable (and me) for a bid when he needs that done, and takes the low bid, as required.
Other small towns: somebody's cousin does it all ,tells them what he thinks ought to be done, and bills whatever they want.
Another town I wanted to bid some work for had it all in one contract 30-40 bigger removals, some really big prunes, and some smaller pruning. We don't do removals, so didn't bid.
Call whoever manages those contracts: forestry department, parks, street department, etc, etc, etc. and tell them you are interested in bidding. I'm pretty sure most places would require that they include you in the bids, but obviously, you'd need to meet some qualifications to win the bid. Ask what those are. You should also be able to see what previous bids where and what the other bids were on the jobs you bid on (depending on state public information laws)