not sure how to prune this rose bush (see photo)
I have tried to research this on the internet, but I haven't had much luck. This rose bush is unusual in that it doesn't have many thorns and is more like a tree in the way it looks (rather then the traditional looking rose bush, having the "canes" - with tons of thorns on them - growing out of the trunk near the ground). As a result, I am unsure about how to prune it when we get closer to Spring. Any help on how and when to prune this specimen would be GREATLY appreciated! I am located in Manhattan, NYC and this is in a container on the roof (the gardener who took care of this passed away not long ago, unfortunately - and left no instructions).