The best thing would be to start with someone established get some experience and idea of if you like it and where you want to go with it. Expensive to train and set up properly. It can be a very quick road to the hospital and the last thing the world needs is another uninsured weekend warrior knackering trees undertaking poor unnecessary work, running away when it all goes wrong etc etc.
I mentor apprentice tree surgeons and we try them all out thoroughly first as it’s not for everyone once you start actually working for a living. Lots of being wet, cold, to hot and uncomfortable with added thorns and sawdust, I think it’s the best job in the world and have been in trees for 20 years now.
Find your local agricultural college, go to the nptc website, read lots on arbtalk and ask a few questions on training in your area.
Read lots on trees as it’s best if you like them and know a bit
I could go on
Best of luck
Nick