Is there anywhere in canon where an animated tree was described and statted?
I think I read this once, but I am uncertain if it was for ArM5. There are so many books to go through.
I keep thinking it was a magical tree Familiar enchanted with something like "Lord of the Forest" ReHe.
Just checking, ArM5 no longer lets Bjornaer have plant heartbeasts, does it? So it would't have been a Great Beast (Great Tree?).
RoP:Faerie displays a "spirit of the forest" creature living in Novgorod Tribunal, with a short mention there is a smaller version in Basque country. It is a spirit being, able to take human, beast or plant forms, but it may fit with the kind of powers you seek.
I'm sure House Merinita grants guidelines to "awaken" plants.
You may look the Herbam elementals/spirits in RoP:Magic too.
(I'm preparing an article about typical supernatural trees in Mythic Europe but nothing official)
Mythic Location/The Cursed Woods have corrupted oak, pine, and willow which will just eat up your grogs. They may be suitable as static enemies and obstacles as written.But to be animated, mobile, and sentient they need changes.
I can't think of any examples in books which are just like Ents. I guess Mythic Europe considers walking trees more strange than trees which can just talk.
The one on RoP:M p129 is accompanied by text saying "These statistics should be used for trees affected by spell such as Lord of the Trees or Calling the Council of the Trees (ArM5 page 139)" so if you're using Rego magics or control by a spirit, this is perfect.