Let’s get out there with a few headcanons I suppose.
Considering Pumpkin-headed folk seem to literally be reanimated skeletons and are led by Enoch, it’s hard to say if they even have souls that he would even be able to turn into trees.
That said, he most likely wouldn’t bother with them if they didn’t. The Beast wouldn’t try to kill them (Considering I doubt he’s the “murder everyone” type), but he certainly wouldn’t like them either. He doesn’t like anyone really.
Also, since Enoch seems to literally be a magical, talking cat, he’s probably predominant in some way at least.
Secondly, The Beast may be fond of “deals”. Now, half the deals he makes with lost souls are only lies that lead to their death (Turning into trees of course), but if anything can pique his interest/he has no reason to want to dispose of them, he might accept a deal.
After all, people have made plenty of deals with death before.
Or if you consider him to be more like Satan, how many stories are there of people making deals with devils?