Hi Dave,
Tree mount information can be found here:
http://www.ronard.com/tree.html
Here's an example of someone's set up:
Normally, you'd remove the top 5 or 6' of a tree so you can get a clear mounting situation and ideally a clear unobstructed line of sight in the direction of the transmissions you want.
Before you get to far into entertaining this scenario though, make a TV fool plot based on the projected height of a tree that would be your candidate do this. The goal would be to gain access to enough signal to make the installation worth it
Cheers.