From the looks of it, it looks like a 'Bear's Paw Fern' or Phelbodium. I can't really tell from your photo's but it looks like it has developed short rhizomes that creep along and are a golden brown color as they age with the newer growth being a light straw color. I'm not sure how it ended up in your tree, but if it was happy there and survived your cold spells, then it must like it there.
