Use the right vehicle
With enough effort, you can get your tree home with any vehicle. But don't risk the headache. Rather than taking the Mazda MX-5 to pick up the evergreen, opt for something more practical, like the MPV in this image.
Protect your vehicle
Even if you have a roof rack for tying up the tree throw an old blanket or some towels underneath it before putting the evergreen up there. The branches can potentially scratch the paint, and it may leak sap. This is a simple way to prevent damaging the vehicle's paint.
Use quality tie-down straps
AAA suggests bringing your own tie-downs, rather than using the complimentary twine that tree sellers generally offer. Ratcheting nylon cords or stretchy rubber pieces are going to offer more strength and are far less likely of breaking.
Point the tree trunk towards the front
When loading the tree onto the roof, be sure that its trunk points toward the front of your vehicle. This is because the bundling process pulls the tree limbs up. Orienting things the other way would have the airflow over the vehicle trying to push the branches down and risk damaging your Christmas tree.
Give it the tug test
Just to be extra safe, give your tie-downs a strong tug before hitting the road. Having the tree fall off in the middle of the road is going to ruin your day, so make sure things are secure before leaving.
Drive slowly and easily
Unlike the Challenger in this photo, AAA advises keeping your speed down when driving home with your tree, like by taking back roads rather than interstates. High velocities risk damaging your newly bought evergreen. If your tie-downs aren't up to the job, then there's a risk of the conifer flying off the roof.
Removing the tree
Now that you're home, don't get too excited to remove the tree and accidentally damage it or your vehicle. Be careful when removing the tie-downs to avoid slamming the ends against your car and potentially beating up the body. AAA also says to check for any sap on the roof and clean it off to prevent from harming the paint finish.