Answer is YES. A couple of years ago, I built a large tree house anchored to one dead and two living redwoods. The main thing is to use bolts or lag screws of sufficient size to ensure stability. You also need to provide additional support for the platform using 4x4 or 6x6 posts tied to your floor joists.
I chose to use a triangular support system at the tree points to increase the span and strength of the support. With three trees, my lateral movement was minimized under most forseeable conditions, so the main thing was downward load strength. You can see from these pics how I did it. GO FOR IT!