Develop a musical piece using the given theme and incorporating the letter-based structure provided.
X:1
L:1/16
M:2/4
K:Bb
['d2 cB', 'de=ef g2c2 c2 z2 F=EFG AB=Bc d2B2']  
X:1
L:1/16
M:2/4
K:Bb
|: d2 cB ABAB | GBAB F2F2 | d2 cB B2AB |{d} cBcd c2 z2 :: BABc de=ef | g2c2 c2 z2 | F=EFG AB=Bc | 
 d2B2 B4 :|  