I climbed up the tree, screwed the strap to the tree with drywall screws (cuz the tree is huge and the straps wouldn't go all the way around it). I made sure there was some slack in the strap. Put a branch in the top of the cam to make it point down. Took some pic's, checked them in my regular camera to make sure the angle was good and adjusted from there with a bigger or smaller branch diameter.. .
If your camera's have the tripod mount hole in the back or bottom, I've used bow hangers to mount those up high. Drill a hole in the end of the hanger and attach the camera to the hanger with the appropriate bolt/washer combo and go screw it into the tree and you can adjust the angle down with the hanger pivot. I use the Mini EZ hangers for this.. You may have to tighten the hanger pivot bolt so it will hold position better.
There are kits on the web that will run you $30-$40 bucks that do this too, but I think these setup's work just as good and the money you save can go for more camera's..