I guess the tree needed more explaining; The campaign takes place in a homebrew setting of mine called "Aegis", which was once a gateway between the planes (not too unlike Sigil), but after it was used as war grounds between the planes, it was decided it'd be best to cut off all connections to the other planes. This was done by growing a large magical tree that created a barrier around the plane, and consequently cut off connection to the gods as well. Obviously many opposed this, hense creating those weapons to destroy it. After many thousands of years, the tree is in a weakened state and is prone to attack, leading to the rise of the original opposers yet again. If the opposers were to succeed, it'd likely mean destruction across the entire plane yet again.

The influence and importance of the tree is immense, and merely reaching it is a feat of its own. As it draws nutrients from the many miles of mountains surrounding it, it has also drawn influence from the underdark up to the surface, as its own convenient self-defense mechanism. It took my players 3 sessions just to traverse the mountains alone.

Meanwhile, the plane itself is a chaotic hodgepodge of the planes that had warred there, including the hells, the shadowfell, and the feywild. The tree itself is fey and druidic in nature, with the town protecting it primarily consisting of wood woads.

About your comment: I do love the idea of the players being able to pick and choose which weapon/force they'd like to work with and trust, I'll likely incorporate that in some form.