VE7GKH has one, it's a little different that what K7LXC described. If you
can picture this:
-where "L" upwards is vertical flat plate to be bolted to the tree (through
bolts with back plate on the opposite side of the tree)
-from the vertical flat plate are horizontal steps at the top and bottom
-"R" is the rotor with "m" mast extending through a "TB" thrust bearing
VE7GKH also has a vertical piece of pipe welded to the back plate into which
he slips a gin pole when he needs to mount or remove his antenna.
With regards to trees dying after being topped, it does happen but if you
use a cap or tree paint to protect the exposed wood it will slow the decay
and eventual death. Another factor contributing to accelerated tree is
excessive limb removal. Trees need limbs...
I hope this helps, of course you need an appropriate bucket truck, willing
tree climber or a really long ladder.