Magic schools!
Are these fine?
Dryadism:The art of linking your life to that of a tree, by feeding it with your lifesblood. The earlier the linking happens in both the lives of the tree and the practitioner (hereafter referred to as "dryad"), the more effective the bonding is, like how you can easily twist the stems of two seedlings around each other, but not do the same with full grown trees. Typically, maximum effectiveness is gained by using the blood of a newborn baby to quicken a tree seed.
After the initial linkage, the bond strengthens over time, and with the amount of care, attention and love the dryad gives to its tree and how well the tree flourishes (meaning that incompetent care is potentially worse than no care at all).
The bond gives both advantages and disadvantages to its participants and is divided into several stages, as tree and dryad slowly fuse into a single entity. The dryad can only perform certain special magical actions known as twistings, depending on the level of the bond, improving its tree over the course of years and decades as it has branches grow in certain patterns and forms runes from the whorls of bark and wood, both inside and outside the tree.
One Life (novice):
The tree and dryad share a single life. Their lifespan is the average of the two's lifespans, so usually the lifespan of the tree would be decreased, while the lifespan of the dryad would be increased. If one dies, so does the other, if one is revived (e.g. resurrective immortality), so is the other. Due to their linked life, the dryad cannot move further than a 500 metres from the tree. If it does, both it and the tree immediately die, and cannot be resurrected.
Example Twistings:
Lesser Improved Growth: The tree grows faster, stronger, better.
Fire-Resistant: The tree is harder to catch on fire
One Body (intermediate):
The tree's body is the dryad's body, allowing the dryad to move into the tree like he'd sink into a bathtub, allowing the creation of more potent Twistings by manipulating the tree from the inside, and allowing the Dryad to hide from potential dangers. Any wounds one of the two suffer is shared by the other, but this does make it somewhat harder to kill them as they pool their collective lifeforce to stay alive.
Example Twistings:
Fireproof: The tree cannot burn from anything but the most intense heat
Improved Growth: Like the lesser version, but better
Longevity: The lifespan is the maximum of the tree or the dryad, not the average.
Bronzewood: Makes the wood of the tree tougher than bronze.
One Soul (Advanced):
The dryad and the tree have a single, shared soul. The tree effectively acts like a phylactery for the dryad, allowing it to be reborn inside the tree in the event that it dies. This still doesn't overcome the distance kill and resurrection limit of the One Life stage however. Magical effects that effect one of the two bonded ones, such teleportation, or hostile magic, effect both, however the dryad and the tree pool their ability to resist such magic, if desired, and the effect is somewhat weakened by having an extra target.
Example Twistings:
Greater Improved Growth: Even better than the other two
Treant: The tree becomes a treant, able to move around and stuff (does not work on Evertrees)
Immortal: Makes the dryad and tree immune to the ravages of old age (redundant for Evertrees)
Steelwood: Makes the wood of the tree tougher than steel.
Tree-Jutsu:The magic of making trees grows faster, better, and more adaptablely. A novice might grow a single tree from seed to adult over the course of a week, and have it enjoy good tree health for the rest of it's life, a journeyman, might be able to make a small copse of trees over a month, with the trees being adapted to taste bad to herbivores, a master could potentially cover a desert in thick forest, that somehow survives in the harsh environment in the future. It's also at the master level that it becomes practical to use Tree-Jutsu in combat, growing trees inside the lungs/flesh of your opponent and so on.
To be able to practise Tree-Jutsu, you must first be in good standing with tree kind (so no lumberjacks basically), and then have a deep understanding and knowledge of trees, as well as make your own body more treelike. Corpomancy is popular to achieve the latter, replacing the skeleton with a wood-equivalent, making your nails into leaves instead etc.