Ask Mr. Smarty Plants

That largely depends on whether you want it inside or outside, living or cut. The roots of an established size evergreen would probably be too big to make it practical to have a growing tree in a pot indoors. If you had access to some native trees still in the ground, there are several that you could cut down and bring into your house. The tree in a pot, if it survived the dry warm air in the house, would have to be removed and replanted outside as quickly as possible. A cut tree, while putting it in water would help and it would certainly be fresher than anything you could buy in a commercial tree lot, is still a dead tree. It could be cut up for compost, or put out to shelter small wildlife until it started to decompose. Unfortunately, snakes count as small wildlife that like to hide under cut greenery.

There are two evergreen trees native to Central Texas and Bastrop County - Juniperus ashei (Ashe juniper) and Juniperus virginiana (Eastern red cedar) - that could count as credible Christmas trees. If you wanted to pot a small one, it would probably make it into your house and back into the ground alive; just be sure not to bring in a male as those are what put out the clouds of intensely allergenic yellow pollen in the Winter. There are shrubs, like Ilex vomitoria (Yaupon), that are small-leaved, evergreen and the females have red berries on them. It would take several years of growing in a pot, trimming and making sure they get pollinated (for the berries) to get something resembling a traditional Christmas tree.

Beyond that, you would need to just use your imagination. You can use just about any potted or cut plant indoors, or growing plant outdoors  and decorate it to your own fancy.