Silas and Zymolxis were both interested in the Incessant Oak trees. Kitla offered to share the Spell with them on a Condition.
Both Necromancers must escape from the Incessant Oak to claim it as their own.
The Incessant Oak is a cursed tree that feeds off of laughter. It grows from a seed cursed with a Valkyrie's Madness and wraps itself around any nearby victims. The tree contorts its victims into heavy and strict poses before proceeding to use any method available to force laughter out of them. Once a tree has fully grown it cannot be chopped down. No force can break the branches of this tree. There is only one way to escape its grasp.
Silas was interested in learning how to cast the spell on his own and wanted Kitla to teach him how.
Zym was interested in purchasing seeds that had already been cursed so he could use them in his dungeon.
Kitla agreed to their requests, but only if they were willing to take on her challenge. If the two Necromancers could escape from the grasp of an Incessant Oak on their own, it would prove that they were worthy to claim the spell themselves. Kitla took both boys into her secret garden and made them her offer.
When both Wizards agreed, Kitla threw down two seeds at their feet before either of them could prepare. The seeds instantly sprouted around them, grabbing the unsuspecting victims and forcing them into new poses. Once the trees finished growing, they began tickling and teasing their victims relentlessly. Kitla took the time to play with their feet before leaving them as they were and headed out of the forest.
Kitla spent the next few days listening to the sweet sound of their laughter drifting through the wind of the valley.
A week later, Kitla returned to her friends who were still stuck in their trees. She playfully teased their toes and enjoyed the musical sound of their squealing. Of course, when she had left them alone, Kitla had purposefully not told them how to escape from the Incessant Oak. It was actually quite simple.
The Incessant Oak is created with very unstable magic. This magic allows the trees to harvest the sounds of laughter and screaming from the area around it and convert those sounds into life energy. This life energy is what allows the trees to live for an eternity, and the energy can even be shared with its victims. The tree will continue to live so long as its victim continues to laugh or scream, but will instantly starve if the victim is able to suppress their own laughter for only a moment.
Kitla was surprised her two friends hadn't managed to figure out how to escape yet. Perhaps they were enjoying themselves in a naughty way and were conflicted about leaving. It's also possible they've been unable to coordinate themselves to stop laughing at the same time. The Incessant Oak makes it very hard to keep quiet for even a moment, and the tree can take laughter from any source besides its own victim.
Either way, Kitla had no intention of helping them out. The Mad Valkyrie intended to enjoy every moment of their Torment.