Make sure you wear proper safety gear and make three simple cuts. Make your first cut at a slight angle, no more than two-thirds into the tree. Make a second cut to form a wedge. Then make a final cut on the opposite side, cutting into the wedge from above. Cut carefully, watch for the wind, and the tree will fall safely away from you.
If vibration causes nuts to constantly work loose, first add a lock washer, if it doesn’t have one. Or, if there is room on the bolt, use two nuts, tightened toward each other so they lock solidly. You can also try wrapping monofilament fishing line under the nut before tightening it on the bolt. Another possibility is to try wrapping the threads first with the teflon tape that is used in plumbing.