Okay so, calling now,
@DragonParadox. The trees that the fruit Shade of the Evening is grown from are modified Weirwood Trees that the Warlocks of the Undying originally were trying to reverse engineer in a similar vein to try to become networked Gods kinda like what their weird sorta half-alive lich forms are now.
The project was deemed a bitter failure but they were able to cut it down for parts and are probably trying to have the same capabilities (divine network) but perfect living bodies, hence clinging to physical forms rather than pursuing the research more.
Alternatively, they wanted to network just like the Old Gods but Valyria's Flesh Smiths took over all the good Leylines and by the time magic was at the low ebb they didn't have theinfluence or power to reach for any of them, as they barely exerted control outside the House of the Undying until recent years.
If we find an Undying plot in Qarth, I'm going to ask for payment for ghostwriting again.