The Tree of Ancients is a non-upgradable building unlocked at level 11. It levels up along with your farm. You and your friends can all add charges to the tree (three times a day for you, once a day for each of your friends, and once the tree is fully charged (but no more than once every 24 hours) you can discharge it for a reward in Vouchers and Kyanite. The higher level the tree generates the more Vouchers and Kyanite. As of version 2.1, Vouchers no longer exist and it has been replaced with Daru and Kyanite.
The energy required to fully charge a Tree of Ancients is equal to 9 plus its level (30 max).