I'm not saying this will work in every circumstance but it could.
The fear you are feeling is natural, so think about why you have that fear, what caused it and what you could have done to prevent it.
You might think you know the answers to those things but knowing and understanding can be two different things.
Since you want to do it again work yourself up to it.
Gain your confidence back in your mind first then go to the foreman/boss/whoever and ask if they will help you after hours to either climb another tree or work towards it. You don't have to spend hours at it, but doing it after hours means you're prepared to give up your own time to help yourself.
Not all bosses will want to stay after hours to help a fellow worker, but some will and any decent boss will see it as someone who is prepared to help themselves for the job they are doing. They might even make time on work time, after all most bosses want to see dedication from their staff not just turning up to get the pay packet
It's worth remembering that each one of the guys you work with has probably had an accident, done something silly, or done something they shouldn't have and only a complete dickhead would try and convince people they haven't, so they know what you are feeling.