Develop a musical piece using the given theme and incorporating the letter-based structure provided.
X:1
L:1/8
M:4/4
K:G
['GA B2', 'c2 BA']  
X:1
L:1/8
M:4/4
K:G
|: GA | B2 B2 c2 ce | d2 G2 GDGA | B2- BB c/d/c Bc | dedB ADGA | B2 GB cBce | d2 G2 G2 GA | 
 B2 BG A2 GF | G2 B2 G2 :: ef | g2 G2 e2 G2 | efed B2 GB | d2 cB A2 FA | c2 BA BGBd | gG G2 eG GG | 
 e2 ed BdGB | d2 dB c2 BA | G2 GG G2 :|  