Thanks! I mostly used John Michael Greer's Ogham discussion in his Druidry Handbook and Paul Rhys Mountfort's book Ogam. Most of my insights came from relentless discursive meditations on the Ogham. There are quite a few books on tree identification that are useful when you are looking into making your own Ogham. You are best going with one that features trees native to your area. I also try to make a point of noticing and talking to plants and trees. The trees will often tell me how they would like to be represented when I am trying to relate their symbols to humans and our dilemmas. My book Sacred Homemaking is going to have at least one chapter about learning to talk to non-embodied beings such as dryads (trees), buildings, objects, and places.