Lv.1 and Lv.2 Trees can be obtained from Desert Chests.
Lv.2 Trees can only be found in Desert Chests Lv.2 or higher as a rare drop.
All Trees up to Lv.3 "Evil Tree" can be harvested for Chomper Stems. They vanish after beeing harvested 2-4 times.
The Lv.6 "Source of Evil" can be tapped once for a number of Lv.1 and Lv.2 Haunted Houses. "Source of Evil" cannot be harvested, but can be merged, however merge results are currently unconfirmed.