In discussing Christmas trees in the comments section here last week, different collection processes were mentioned. I didn’t know of Utrecht doing anything specific, but now it turns out that Utrecht is part of a pilot program to process discarded Christmas trees into green energy. During the first two weeks of January, the trees will be picked up and processed separately, and then sorted and shredded and so on, with parts of the trees becoming biofuel and the rest becoming compost.
It seems that Christmas trees are usually difficult to compost, since their wood is hard and takes too long to break down. Many of them end up in the incinerator, which then produces CO2. With this new process, they can be broken down and used more effectively, with the ultimate result of producing more electricity than they use.
You can read more about it in an article here (in Dutch).