Bone Pile

Bone Pile can be harvested from (Pile of Bones with skull).

Bone Pile can be tapped to create 4 Bones, which can then be merged or harvested for Level 1 Trees of Life.

You can also drag a creature over to harvest a bone pile. The bone pile will not always shrink when harvested, but will disappear if it shrinks twice and then is harvested again. At its smallest, a bone pile can still be tapped for 3 or 4 bones, increasing the value.