If these stems are hollow check out Pokeweed (Phytolacca americana). Until the plant is flowering, I’m not at all confident with these speculations. http://www.midwestnaturalist.com/phytolacca_americana.html

Information link for redbay (Persea borbonia). http://hort.ufl.edu/trees/PERBORA.pdf

It’s hard to tell without its flowers. As this grow more mature, please give us an update. For now I could only speculating, maybe something in the Persea genus? Avocado is in this group, although it’s tender in your zone, I’m unable to tell more. Check out a species in the group from the included link below, the redbay (P. borbonia). Click on images to enlarge. Until it flowers, I’m only speculating. Best wishes! https://www.invasive.org/browse/subthumb.cfm?sub=3313