There are multiple ways to have a zero waste Christmas tree. Here are some options for you if you're trying to green-up your Christmas!
Acquiring The Tree
Cut your own!
Here in Colorado we have the option to pay $10 to go cut down a tree from most National Forests. The tree must be 6 inches or less in diameter and cut 6 inches or less from the ground.
Christmas tree cutting is done in designated areas and helps mitigate fire risk!
Find it Local
I know this isn't possible for everyone. But if you can find a tree at a local Christmas tree farm, or at your farmer's market, these are more likely to not have been trucked for thousand's of miles to reach your household.
Plantable Trees
You may be able to buy a living evergreen tree w/ the bulb at your local gardening store. After the holidays are over, take it outside and plant it!
Artificial
I don't recommend artificial trees, simply because they can contain PVC or lead and are often made in non-fair trade factories abroad. However, if you really want one, I'd recommend finding one used or vintage!
Non-Traditional
The possibilities for non traditional trees are really endless! I recommend doing some searching on Pintrist for inspiration!
Zero Waste Christmas Tree Ornaments
Popcorn Garlands - my DIY
Also a super easy (and yummy) decoration! I made a bunch of stove-top popcorn, and invited a few of our friends over for a couple drinks and garland making! It was easy and really fun!
Felt Garlands - DIY
Christmas Lights
Oh dear, Christmas lights.
This was by far the hardest thing to figure out how to do, and I'll admit my own solution was not perfect. Second hand Christmas lights usually aren't working correcting and can take a significant amount of time to go through and find faulty bulbs.
What I'm trying for now are minimal-plastic LED lights. These are more energy efficient, and should last for a very long time! While they are not plastic free, they are not insulated the same way that traditional lights are, so they have much less plastic.
I think you could go no Christmas lights if you're feeling committed to the cause. If anyone has a better answer to this particular problem I'd be happy for the suggestion!