While neither are great for your cat if they start munching on them, real trees are actually a bit more dangerous. So you need to make sure this is completely inaccessible to your cat. You can also try putting tin foil around the trunk to deter climbing if you have a kitten.
Shorter is better! A tall tree crashing down with a kitty in it would be much more catastrophic. You could also try doing some smaller trees safely sitting on tabletops out of reach instead of one big tree.
Make sure the tree is in an open space – away from any shelves or furniture that your kitty could jump from. You could even try using a small table as a base for a larger tree just to put it a little out of your cat’s reach.
Lights can be another source of danger, so make sure you tape down any dangling wires. You can also find some Christmas tree lights that shut down if they are damaged, which would reduce the risk of a chewing kitty getting shocked.