The North Bierley branch is so called because that's where its members were living in the second half of the 19th century. It's believed that they originated in Bradford, however. There were many BARTLE families in North Bierley around this time, to one of which, the Leeds and Wyke Branch, this branch connects.
There also seems to be a strong connection between the North Bierley BARTLEs and the Shelf Branch, although we haven't figured out the details yet.
To become a member yourself, contact the co-ordinator. Don't worry, it's free!