Develop a musical piece using the given theme and incorporating the letter-based structure provided.
X:1
L:1/8
M:2/2
K:D
['AF dc BG', 'ge fa df']  
X:1
L:1/8
M:2/2
K:D
 AF dc BG dB | AF DF E2 E2 | AF dc BG ge | fa Ac d2 d2 :: AF ge fa df | cA ge fa df | BG Bd cA eg | 
 fa Ac d2 d2 :|  