It definitely sounds like fleas - this happened to me many years ago, the fleas were laying eggs just under the edge of the sofa, and as soon as a warm person came by (i.e. me) they hatched and bit.
You need to get to the vet and buy a really good flea spray and spray everywhere, not just where the cat goes.
Your flea treatment doesn't sound good to me - why are you bathing him in tea tree oil? - that's quite unnecessary, cats don't need bathing every month, my cats are over ten years old and have never had a bath in their lives. Get Stronghold or Advocate, a proper chemical flea treatment, and use that every month. No cat needs a bath or daily flea-combing.
It's interesting you say that the bites are happening while the cat's not there - this is exactly what I found. The cat was away so the fleas had nothing to jump on except my ankles. It's fleas.