While some traditions have the Oak King reigning from the Winter Solstice to the Summer ones. Others do the opposite. To me the Holly King rules from winter until summer and the Oak King ruling from summer to winter. The reason being is holly, mistletoe, evergreens, etc time of brightness and flowering happen in the colder months. While Oaks, other trees, flowers, grass, etc grow bright and flower in warmer weather.
Here is a link for a general search of the Oak King vs the Holly King of you want to read more about the : https://www.bing.com/search?pc=GIWI&form=AMZNS2&q=oak+king+and+holly+king