Besides I kill plants. I can kill a cactus. I did kill a cactus. I kid you not. It drowned and rotted.

Don't feel bad about it. It a myth that cactus are easy to grow. Cacti are actually quite difficult to grow outside of their home territory. Here they can get sunburned and die. Where you live it's next to impossible to give enough of them enough natural light. It's difficult to tell whether they are getting too much or too little water till it's too late... A lot of cacti bought from big stores are dying before you get them through the checkout because the store didn't know how to take care of them.

Enjoy your tree while you've go it and don't worry about what happens after Christmas. ;o)