Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/8
Q:1/2=80
M:2/2
K:G
['Bd (3BAG', 'g2 dB']  
X:1
L:1/8
Q:1/2=80
M:2/2
K:G
 d2 Bd (3BAG Bd | Bd (3BAG cAAc | Bd (3BAG Bd d2 | Bdce dG G2 ::{ef} g2 dB g2 dB | 
{ef} g2 dB cA A2 |{ef} g2 dB g2 dB | B>dc>e dG G2 :|  