Trees on a Pole

I saw this or something similar to it all over the place in Slovakia. We'd just be driving (or walking) along and all of a sudden there'd be this fir tree completely covered in ribbons and sitting on top of a really long pole. When I initially asked my local hosts what those things were, they didn't know what I was talking about. Five minutes later we saw one on the road and they were able to explain to me that it's related to May Day celebrations somehow. You stick the poles either in front of local government buildings or by the house of a single woman. The connection between the two was not elaborated.