The Medusa Tree is not called after certain mythical beings, but rather after common sea medusae. It does not look very akin to them, having numerous “tentacles”, actually thin branches, covered with many fuzzy leaves, that move with the faintest gust of wind, giving the whole tree a somewhat unclear bush-like appearance. But so far, there is nothing special.
The actual reason why is it called after medusas, is his power to deter any hostile creatures, and to be sure, all creatures:
A) The leaves exude a chemical or biological substance that is aggressive to most living beings. Effects range from a mild rash, through paralysis up to death for the really unlucky. Of course there are a few creatures immune to the allergen by now.
B) The tree has the power to assault visitors with electric shocks (or for fantasy, some sort of magical shocks might be also possible), strenght depending on the contact one has with the leaves. Of course, the wood of this tree would be highly sought after for certain magic items, and hard to get.
C) Looking like a strange, but common tree, it is actually a metallic lifeform, growing out of depths of the world, slowly and tirelessly. The electricity comes from it’s “roots” reaching miles below; so this is actually the lifeform’s ofshoot. Should the root be broken (due to earth movements, for example), it will wither away into a pile o rust within days. Understandably, it is very rare, considered even unique and an important omen by some folk.
The tree itself is not sentient, it is just growing very slowly, and found a means to protect itself from the surroundings.