A quick web search revealed a lot of answers -- and I mean a lot. Tea tree oil has some healing properties, both "magical" and medical. It is at least mildly antiseptic, and has been used in healing spells by some. Of course there are more uses.
Before you take any and all advice you find online: It is not advised to take tea tree oil internally. Also, as far as flea sprays are concerned, beware that some essential oils, even in small amounts, can be harmful to cats and some dogs.