I don't think anyone uses Spirit Tree. Even when CoV launched and we weren't overpowered deathballs, the buff was just not that good, the recharge too long.
It's also a really weird power. It's a pure buff power, but it's in a Control set. It's theming seems totally at odds with the rest of the set, being some kind of mystical, ethereal ghost plant. And it makes the same sound effect as Blazing Aura, a fire-themed damage power. Just top-to-bottom, a bizarre power.