REGISTER NOW Cambridge Savings Bank is borrowing from the playbook of larger rivals as it looks to add customers from outside its Boston-area footprint. Like the $187 billion-asset Citizens Financial or the $135 billion-asset MUFG Union Bank, the $5.2 billion-asset Cambridge Savings has launched a digital-only bank with a goal of attracting depositors from across the U.S. Dubbed Ivy Bank, the new digital-only unit offers savings accounts and certificates of deposit, but its menu could expand as it adds customers, said Katie Catlender, the bank's chief commercial officer. “What we intend to do is just watch and learn and really look at what people need next,” Catlender said in an interview.