Moni

Sure, they could be fungus gnat larvae. Do you have the adult gnats flitting around your tree? There are a number of things you can do for fungus gnats. If you spray, Insecticidal Soap or Neem will work just fine. But you have to spray many times (follow the label directions) to get all of the potential generations. There is a BT that works on the larvae. You use it as a soil drench. Go to any local nursery and ask for it. They will know what you are talking about (at least they should) whether they have it or not. I use that and I use yellow sticky traps to trap the flying adults. It works pretty well and you are getting both the adults and the babies all at once.
Moni