I dont know what kind of tree it is, ficus maybe, i don't really know for sure, but if it has gone from being brown to lush green, i would keep it inside where it is. You cant just force a tree outside when it's been inside, the frost will shock and probably kill it. I would keep it inside if it is thriving inside, which most outdoor trees will not do for long. I agree it is probably a tropical and in your area is probably best grown inside. I would not just stick my tree outside and hope it survives a random drastic change in temperature, if you are going to put it outside, at least wait until the last frost is over, if it is supposed to go dormant in the cold, do so next winter, it will have time to adapt to the cold then, as for now, don't rush into it. oh and by the way, nice tree
