TOPIC:

Ok, that's a slight exageration, but my bars and the guages, headlight etc. are all pointing a little to my right when going straight. I never even noticed it (my first bike) but a buddy of mine who's ridden all his life showed me. He said all I need to do is put the left side of my front tire against a good tree and yank the steering to the Left until it straightens out.
That sounds a bit too caveman for me.
Question is: should I do the tree thing, or should I loosen everything up and try to straighten it and tighten up all the bolts???

By the way, the bike rides great at all speeds...

Your buddie's method would appear to be taking "shade tree mechanics" to the extreme. I would not advise it.

I have used your buddies method several times over the years, but I don't yank on the bars, just apply steady pressure.

It's not the right way to fix it though

I actually did it (my own version) and it worked. On the centerstand, I straddled the front wheel with my legs, and gently turned the bars in the opposite direction from where they were pointing and it straightened out. I've ridden it about 50 miles since and it's still straight.