By far the better option is transporting the tree using a roof rack: not only does this make it easier to secure your tree, but it also adds a few reassuring, additional centimetres between the needles and the car's paint finish. In principle, it's helpful to have two people to position and secure the tree on the roof rack, as then the tree has less play while it is being attached. Securing the tree for roof transport is much the same as for transporting in the boot: first wrap the trunk, then the whole tree using the lashing straps, and then tie it tightly to the frame on the roof.
To ensure that the tree is clearly visible to other road users, the red flag on the top of the tree, or the red flashing light and reflectors, are a mandatory requirement even if the tree is transported on the roof of the car. To be absolutely safe, be sure to sit behind the wheel before setting off and check your own field of vision through the rear windscreen.
Save the tree!
Only strong lashing straps or tensioning straps are suitable for securing loads such as a Christmas tree on the roof. One absolute no-go are bungee straps (thick elastic ties). In an accident at 50 kph, the forces acting on a 32 kg tree give it an effective weight of 750 kg. An elastic bungee strap cannot cope with that strain, meaning that the tree turns into a dangerous projectile. Even sudden braking manoeuvres can present a risk.
If you follow this advice, you should get your tree back home in relaxed fashion. And once your Christmas tree is standing in your living-room, its fragrance filling the air - then, if not before, the comforting, unique feeling of Christmas envelops you. At that point, the Christmas tree ritual was once again worth the effort this year.