Develop a musical piece using the given theme and incorporating the letter-based structure provided.
X:1
L:1/8
M:2/4
K:G
['gdBd gdBd', 'gdBd gdBd']  
X:1
L:1/8
M:2/4
K:G
 d | gdBd | gdBd | gabg | afdf | gdBd | gdBd | edef | g2 z :: A | A2 df | e^cAc | d2 fa | ge^ca | 
 agfg | agfb | agfe | d2 ef | gdBd | gdBd | gabg | afdf | gdBd | gdBd | edef | g2 z :|  