The central and most powerful card of this deck is Mulchmuncher, a massive 8/8 minion that gets cheaper for each dead treant. Here you have enough treants for it to become a 0-mana minion, which is really powerful.
Cards like Witchwood Apple, Landscaping, and Soul of the Forest can generate loads of treants that can be buffed using Power of the Wild and Tending Tauren. Dendrologist, a brand new card from The Boomsday Project, also fits this deck just right.
Lastly, if you need to protect yourself, then use the tried-and-tested Spreading Plague plus Strongshell Scavenger combo, or just play Giggling Inventor that summons two Annoy-o-Trons.