As a qualified Tree Surgeon here in the UK I have 4 chainsaws altogether. I make my own chain from a 50 foot roll of chain. I am able to make them at different lengths for the different size bars I have on my saws. as for climbing trees here in the UK we are required to have passed the relevant climbing qualifications with the proper equipment. I read earlier about using a Fall Arrest System as used by scaffolds. I believe this is ridiculous as if you have decided to use this system as a decent height then have a fall it would be near impossible for anyone to rescue you. My training has also included Aerial Rescue allowing me to rescue anyone who has gotten themselves into a position where they are unable to make their way out of the tree.
I have watched many You tube vids of idiots around the world doing what they think is the best way to remove tree limbs or take down the whole tree with disastrous results. I think there is a common level of intelligence amongst them all.
When climbing a tree I always carry a hand held pruning saw, which is used probably more than the chainsaw, unless of course there are big limbs to remove.
here is pic of the type I use.