I taught myself to climb and the others who have posted so far are not joking. Its dangerous. Knowing what I know now, I sometimes shudder at the things I did and managed to get away with on the first few trees I climbed. That said make sure you:
#1, arm yourself with knowledge, watch youtube videos of climbing, find a qualified instructor/mentor, read the Tree Climbers Companion by Jeff Jepson (best reference for beginning climbers anywhere).
#2, Get the right gear, dont skimp out on a $100 set of rusty old linemans gear you see on ebay. Probably the best kits I have seen are sold at
wesspur.com and these include all the climbing gear you will need as well as a free copy of the Tree Climbers Companion. You can always sell it later, don't trust your life to used old gear you know nothing about. Don't forget about basic safety gear as well, helmet, safety glasses, chaps, hearing protection.
#3, Practice practice practice. Try out your gear in a tree you plan to remove. From a height of less than 15' practice ascending and descending, clipping in your lanyard to position yourself. Get comfortable leaning into your ropes in a comfortable working position at a low height before you move on to using actual tools at heights. Get comfortable on your spurs if you get them to do your removal. Go up and down as many times as you need to without tools to get the feel of moving about the tree in them.
This isnt a small undertaking as I am sure you know. The safe route would be to hire someone to do this who knows what they are doing. But if you are set on learning to do it yourself then follow the guidelines I have set above and use your common sense. Best of luck and be safe! There are many members here who would be happy to answer your questions along the way if needed, use this resource!