Unauthorized tree climbing CAN be a gateway to depravity.
Sounds to me like you were the Nazi Germans, and he was way out over enemy lines, and merely scouting you out, or at least that's how I would have thought at 8 or 10 years old.
When I was an 8 year old, the whole neighborhood was my yard. I didn't are about property lines, just finding the best spot for collecting acorns, or following my dog. The place was kind of Leave it to beaver-ish, with all the moms home and keeping an eye out for each others kids and all, but it was no big deal to climb someone elses tree, or hop in their pool if they were on vacation.
I knew everyone in the neighborhood. Most of them were my customers on my paper routes, or I nowed their lawn or blew theior leaves off in the fall or shovelled their driveway in the winter.
Why is it such a big deal if a kid is in another neighbors tree? Why would you even care. He wasn't doing anything especialy wrong. He was probably on a super important spy mission, or hunting terrorists in his own way. The imagination of a boy knows no bounds, especially some stupid arbitrary ( to a kid, anyway) property line.
If there were people in my neighborhood who got eggged on halloween, it was the busybody people who did what they could to stifle the development of a kid, and who had real wussy kids themselves. That's not to you are that way.
...it was no big deal to climb someone elses tree, or hop in their pool if they were on vacation....
Ahh, the days before injury litigation while using some one else's property without permission.
Unauthorized tree climbing CAN be a gateway to depravity.
But, sadly, things are not that way any more.