Feast of Deliverance

The Feast of Deliverance is a great Elven festival that celebrates the return of spring and the saving of Aenarion’s children from the forces of Chaos by the Treeman Oakheart. Without his intervention, Yvraine would not have survived, and thus, there would be no Everqueen. So the people of Ulthuan hang green paper lanterns from their houses, and place carved statues depicting a friendly cross-between an elf and a massive oak tree in veneration of the heroic Treeman.

Source

 * Blood of Aenarion (Novel)
 * chapter 5