code for mounting conduit and boxes on a tree
225.26 is all I can find.
The main thing to be concerned with is not the tree growing up, but out. UF stapled to trees is the worst. As the tree increases in diameter, the staples stay put, and the tree pushes the UF out until the staples cut through the insulation.
I remember some sage advice I heard a long time ago. Use RMC only, use stand-off straps, and keep the screws slightly loose.
Nevertheless, I like to use PVC on really gnarly trees, like the live oaks that grow here in TX. If you have a large hotbox, you can form the conduit to the most convoluted trunk shape. It is as natural a look as you can get.
