Both of these are correct.

According to the "Chinese Flower Classic", the other name of wintersweet is wintersweet. At the same time, "Flower Mirror" also records: "Wanmei is commonly known as wintersweet, also known as yellow plum. It is not a plum. Because it blooms together with plums, its fragrance is similar, its color is like beeswax, and it blooms in the twelfth lunar month, so it got its name."

So, it is correct to call it "Wanmei" or "Wanmei".