They are ancient, human knights, who shape-shifted into huge trees. According to Flora, they are full of life in just a single touch. According to Miele, they are good-natured beings. Since Selina awakened them from torpor, they must have fell into deep sleep from long ago.
"The ancient knights, who took the shape of huge trees."
In "The Flying School", Selina awakens these beings against Linphea. They kept Linphea's fairies and warriors hostage during the Winx's fight against the witches.
Next episode, Flora, with her new Bloomix powers, stabilizes them.
They have shapes of huge trees (as the story) with branches on their head and two branches in two sides of each one as hands, but there are only leaves on the branches that are not their hands. They can walk on their roots (if awake). Their eyes are red if evil because they are ordered by Selina via the Legendarium but brown if asleep. They have beards and faces of elderlies.
According to Daphne, their weakness is their roots. Once the roots are firmly planted into the ground and made contact with the soil, the treants will re-stabilize.
- In Season 4 the Amazon Fairies used their magic to turn trees of the Amazonian Rainforest into humanoid Treant-like creatures.
- It is unknown if their eyes are red and evil when they're normal like when they are ordered by Selina via the Legendarium.
- It is unknown who those ancient knights were and why they took the shape of huge trees.