Hi starone,
I'm guessing you probably have musa basjoo which is the hardiest of the bananas, as it comes from alpine areas of Japan. If you google that name and then click on images, it will give you some idea of the size you can expect.
I grew one of these at my old place and it was a conversation piece for anyone passing by, its leaves alone can be 6 feet long!, mine reached about 16-17 feet in height.
Botanically, it's actually a herb rather than a tree and will die down at the end of the growing season and sprout up again next year with a fresh clump of stems, as thick as your thigh. Sometimes known as the walking tree, because it will come up in a different place every year.
Although reasonably hardy, it will need some protection from frost, over the winter, I used to cut the stems down then use the leaves as a mulch to protect the area around the roots.
Mine flowered one year and I had some small (unedible) fruits which was very unusual to look at. The flowers came out on a kind of arm, which snapped off in the wind.