She is voiced by Caitlin Prennace in English.
Treesa is very calm and has a very peaceful endeavour to her, fitting of a nymph. She seems to be very merciful as well. Being a tree nymph with tree-like qualities to her, she holds a big respect and care for nature, so much that she's dedicated her entire life, for centuries, to protect and take care of a single garden, along with her sister Thorna. She's satisfied with this life and doesn't have any plans of changing it in the future.
Treesa is a gigantic ghoul, that mixes well with the trees in the forest. In fact, her body is made of wood, in a brown hue. She also has noticeable wood grain texture all throughout her body. She has long spindly arms, with several branches sprouting out, like a real tree. Her legs are also long as thin, and seem to be able to take the form of a tree trunk at will. She has green vines branching out her back all around, like a peacock's tail. She has hazel eyes, and curly burgundy hair, down to her shoulders, with electric green highlights.
Treesa is the older sister of Thorna Thornwillow. Together, they've protected their garden for centuries and have gotten used to that life together. Treesa cares very deeply for Thorna, getting worried when Thorna goes rogue, but showing compassion, as she understands Thorna's wishes of freedom and condemns herself to protect the garden alone, by giving Thorna wings to fly.
Treesa seems to have history with Venus Flytrap, as both recognize each other on the other side of the flower intercom.
- December 25, 2015: Treesa Thronwillow's images are revealed through a leak in the Swagsbucks survey, along with the Garden Ghouls line.
- July 31, 2017: Treesa Thronwillow's profile is published on the Monster High website.
- October 11, 2017: Treesa's webisode appearance becomes known due to an early preview release of "Garden Ghouls" on the Monster High website.
- October 13, 2017: Treesa makes her cartoon debut in "Garden Ghouls".