Yes Tea Tree Oil can treat cold sores but before applying the Tea Tree Oil to the cold sore you should dilute it with some carrier oil such as olive oil because applying Tea Tree Oil and any other essential oils directly to your skin could cause irritation to the skin.
Once diluted you can apply the Tea Tree Oil to the cold sore 3 to 4 times per day using a cotton Swab or cotton ball and over 3 to 4 days the cold sore should go away.
You can also treat cold sores using Apple Cider Vinegar applied directly to the cold sore 3 to 4 times per day.