The result isn't quite what I wanted (the "Rooting" ability turns out to have its own model and animations, and it only activates one type, so it can't be applied to other creatures because when activated, it changes the creature's model to that of an Ancient Ent). I had to replace the third "Rooting" upgrade with "Endless Retaliation."
So, in the end, we have the first upgrade as "Ent," the second upgrade as "Dendroid" and "Ancient Ent," and the third upgrade as "Dendroid Guardian" and "Wild Ent."
The Ent was not changed.
The Ancient Ent was not changed.
The Dendroid repeats the characteristics of the Ancient Ent, but instead of "Rooting," it has regeneration of 50-60 HP.
And the third upgrades were quite ambitious, but their cost is no longer 1400, as with the 2nd level, but 2800, which corresponds to the parameters.


Dendroids


Wild Ents
Since I renamed the "Forest Fury" ability and applied it to the Elementalist and Elemental Warrior's center perk, I removed it from the Wild Ents, compensating them with the same characteristics that this skill gave them (-50% defense, +50% attack, +5 to initiative).

Thus, we have two upgrade paths, one focusing on defense and resilience (regeneration and protection from the Disintegration Ray), and the other focusing on attack (increased attack, high initiative, protection from slowing).
That's it, write your feedback, I'll be glad to hear your opinions.