I'm sure that plastic or other artificial trees aren't so adapted to freezing, especially by nitro-glycerin.

Especially when you start plugging in stuff like those annoying singing Christmas lights. I'm sure the tree would spontaneously combust to put itself out of its own misery.

Surely something else could have been done to cap off a series on things frozen in liquid nitrogen--

if pikrete, frozen water-saturated wood fibre, is evidently so strong, why would you expect a "2 thirds water" bundle of cellulose to explode?

And would anyone volunteer to dunk a Christmas tree in a big tub of liquid high explosive?

If all else fails, why not just water the tree with a mix of water, gas, hydrogen peroxide, rubbing alcohol, and fine gun powder for a few days....just lets say..."accidently mistaking it for ordinary water"....then what say one of those typical office style long tubular lights blows out creating a large spark that just so happens to hit the chemically watered tree.....hmmmm......the chems will likely make the tree get ugly as all heck, but atleast it will have a chance to absorb some explosives into its trunk and roots. In other words...just find atleast a fun way to blow the dang thing up! lol.