The Ancient Tree is a purple tree that randomly grows approximately once every 20 to 45 minutes containing Logs and a Rare 
Snake Eye.
Woodcutting
Ancient Tree's can be chopped in order to gather any logs currently in the game (based on your woodcutting level), and when you're lucky a rare Snake Eye.
Rewards
Aside from Logs that you can chop at your respective Woodcutting level, you can also find a rare Snake Eye which can be used to craft the:
Locations
Can be found anywhere in Brightleaf