What Kind of Tree Is This?
It is probably a paulownia (or maybe a catalpa). I have one in my yard also, kept cutting it down every year and finally decided to let it grow and discovered then that it was a tree. They stain things that are underneath it, so dont keep your garden chairs...
What Is This Garden Plant?
As long as you dont eat it and dont have kids that might be inclined to eat the berries, it is safe enough. It does have beautiful little purply-blue flowers.