This is what NIH has to say about tea tree oil:
https://www.poison.org/articles/tea-tree-oil
It is poisonous if swallowed, and can have adverse effects even in small amounts.

IF TEA TREE OIL is used in the mouth, it should be spit out immediatley, and the mouth rinsed. Don't leave it on the gums where it may be accidentally swallowed with saliva.
Tea tree oil has demonstrated antibiotic properties, but as an antifungal it was no better than a placebo.
Sue