I don't know for sure since I haven't read or watched it. But it could be a young couple who find love around a Christmas tree.
There might be a man and a woman as the main characters. The man could be someone who has a special connection to Christmas trees, like he grows them. The woman could be a city dweller who comes to the countryside to get a real Christmas tree and they meet and fall in love. There could also be an older character, perhaps a wise old man who has been around Christmas trees all his life and gives advice to the couple as their love story unfolds.
Since we don't have much information about this 'cast of a christmas tree love story', it's difficult to say exactly who the main characters are. But we can assume some typical characters. It could be a couple, let's call them Jack and Jill. Jack could be a Christmas tree seller, and Jill could be a customer. As Jill is looking for the perfect tree, they start talking and gradually fall in love. There might also be a supporting character, like Jack's grandfather, who has passed down the family Christmas tree business to Jack and has his own stories and wisdom about love and Christmas trees that influence Jack and Jill's relationship.