Bridal Day
Bridal Day was an annual event held by the humans living on a future colony planet of Earth. The celebrations centred around the forest elders choosing a young woman to be dubbed the "forest bride", in which she would be absorbed into a tree to provide good fortune for the people. Most forest people considered this an honour, although Monnay was terrified at the prospect. The celebrations were often marked with singing and dancing all day among the people of the forest.
Upon discovering another woman due to be sacrificed and saving her, Yasmin Khan was chosen in her place, but was eventually rescued alongside all the other former brides, except for Monnay, who had struggled against her capturing.
In truth, the ritual stemmed from the trees' positions as hidden stasis chambers in times of crisis whose real meanings had been lost over a very long time. The Thirteenth Doctor helped the people to stop the sacrifices upon discovering this. (COMIC: The Forest Bride)