I had feral kittens dying from a flea infestation. They were too young for treatment with commercial remedies, and tea tree oil can KILL cats at any age. As a nurse, we once had a patient who had head lice infestation that we couldn't rid of with prescription treatments. The CDC recommended olive oil left in for 4 hours and then washed out, so I decided to try it for these little (less than 3 week old) kits.
Please never use tea tree oil on cats as they cannot handle it in their systems.