Well, dryads are technically fey too, so you could use that angle, but I guess it depends on how it is presented. This would be the second undead fey-plant in the game so far (at least that I can remember), the blackroot treant would be the first.
If I could make a guess, it's likely related to the Dryad's tree.
[sblock=Tangent]In my game, I have a Wood Court (Wood Elementals/Sentient Plants and Fey), who are allied with the Ghoul King, a powerful ghoul shaman that rules a tribe of cannibalistic humanoids.
One of my players couldn't get why plant elementals, very Nature-oriented, would ally themselves with something Undead, since Undead is very outside the natural order of things.
Of course, what he
didn't know is that the Ghoul King and his tribe were hyper-vigilant about killing hyena. Hyena, in my campaign, are pre-gnolls; if a hyena eats a man's soul, it becomes a gnoll. Gnolls then capture victims to spread their numbers, and they venerate demons, trying to bring demons across. Demons are corrupted elementals, who try to corrupt everything, so they scare the bejees out of elementals.
... I confess, my campaign is very supernatural-politics. To the point I am afraid it's too much for my players, who are constantly confusing different groups.
Note to self: Figure out what happens when a Demon gets ahold of a Fey and corrupts it.
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