My own experience is limited but all I did was take a nice dry piece of apple wood and cut it off my tree. The branch had been dead about a year at the time. I removed the small amount of bark still clinging to it, scrubbed it with a brush in the kitchen sink and screwed it to a piece of slate with a stainless steel screw. I have now had it in my endlers colony tank with some java fern attached to it for a few years with no troubles.
A few key points, I know I don't spray my apples so no chemicals to worry about. It had been dead and air drying for over a year so no sap to worry about. Apple is a very dense hard wood so it was fairly easy to get it to sink with just a bit of weight added by the slate. Fruit woods are fairly safe in terms of any chemicals that might leach out of the wood if it were not properly dried.
