>>35172879>resembles a treeIt what way? Do you even have eyes? It looks like a clump of wires. If we're counting it's rooted state, I'd be a hell of a lot more quickly to claim it's some kind of starfish than a tree.
Celesteela and Nihilego work because they resemble specific things, br behave differently and have different types as a result. You expect grass for Celesteela, but it's a machine that acts like a plant. You expect water for Nihilego, and you get a living glass construct that flies around in dry land.
Xurkitree looks like a bunch of wires that saps electricity and... that's pretty much what you get. It goes halfway through with the plant thing, but only through lore tidbits and its name- nowhere in design. They should have gone all the way through with it, opting for an Electric/Grass bunch of wires, that actually turns out to be a plant when you get right down to it.
And it's clear that this is what the conceptual artist had in mind, judging by their notes. But Gamefreak hates stealing away Rotom's precious type combos, so they left a potatially better concept as another boring pure Electric.