You've been given a lot of good advice here, take it.
When you've got your kit, read Climber's Companion five times, have figured out how to go up and down without ever being unsecured...come down and start again.
Then get a good idea of how wood reacts when it is under different loads, tension, compression, side loading. Then learn what cuts and what sequence of cuts to make to remove a loaded piece of timber safely. Do this with a handsaw FIRST. You make one ****oo with a chainsaw and it could well be your LAST.
Learn what defects in timber mean for your climb and cut plan...oh, you have to learn to recognize defects first...
Whenever you think you are ready to cut something...STOP...think, 'What will happen if this goes wrong?'
Where will the piece of wood go, where will your saw go, where will YOU go and will any of the other things hit you on the way past/down?
It may mean you rethink your strategy, take a few more seconds or even minutes to attain a better position, but when the inevitable F*&%up happens, you will survive, intact, or only with minor injuries.
I ALWAYS take a moment to make sure every part of my body AND my climb line and lanyard is OUT of the way of follow through, kickback and the piece of wood falling. IN the tree follow through is as dangerous as kickback.
And yeah, until you know when it is Ok to use a chainsaw onehanded, DON'T!
Start SMALL, start LOW, and start with a handsaw.
Did I mention to read Climber's Companion five times?...don't leave out the introduction either.