Tree of Undergrowth

Whenever a creature enters the battlefield under
your control, you may look at the bottom card of
your library and you may put it onto the top of
your library. If you don't, exile it and put an age
counter on Tree of Undergrowth.
Sacrifice Tree of Undergrowth when it has ten or
more age counters on it and you gain 10 life.
Things emerge from this tree that no one is able to
explain how.