This deck is built around the fact that Tom Bombadil describes himself in the following words, "Eldest, that's what I am... Tom remembers the first raindrop and the first acorn" and yet Celeborn refers to Treebeard as "Eldest" and Gandalf says Treebeard is "the oldest living thing that still walks beneath the Sun," so which is it?
I did take the creative liberty in assuming, or imagining, that Tom and Treebeard were at least aware of each other, even if they hadn't actually ever met. I also assumed that the included Lore or Neutral allies would have encountered one or the other of the heroes during their lifetimes, as either long-lived elves who loved trees, ents, or woodsmen.
Mechanically, the Rivendell Minstrel can fetch songs to boost Tom's willpower, while Thalion can become a hero with the side quests provided (since Tom seems like a side quest kind of guy).
I didn't include the items in the sideboard, after some consideration, because they seemed to be too disconnected from the theme, even if they were useful.