The Garden Club of the Back Bay on Thursday dedicated a cherry tree on Beacon Street in memory of two Boston firefighters who were killed while battling a nine-alarm blaze five years ago. A plaque at the foot of the tree bears the names of Lieutenant Edward J. Walsh Jr. of Engine Company 33 and firefighter Michael Kennedy of Ladder Company 15, who lost their lives on March 26, 2014, while fighting a fire at 298 Beacon St. in the Back Bay. “As this tree grows and its roots become stronger, so shall the memory of their sacrifice,” the plaque reads. The tree, fence, and plaque were donated by the garden club.