Certified GKH Gardening Expert
Unfortunately, your photos did not come through. It sounds like new, healthy growth. However, if this is growth that originates from the base of the tree and is not weeping in nature, then it could be a shoot from the root stock. If this is the case, it should be removed.
This article will explain tree reversion:
In the meantime, these articles will help you with the care of Birch trees: