Develop a musical piece using the given theme and incorporating the letter-based structure provided.
X:1
L:1/16
Q:1/2=60
M:2/4
K:Bb
['B2 B4 Bd f2 f4 ga', 'F4 f2 f4 df g2 e4 de']  
X:1
L:1/16
Q:1/2=60
M:2/4
K:Bb
 B2 B4 Bd | f2 f4 ga | b2g2g2e2 | e2c2c2A2 | B2 B4 Bd | f2 f4 ga | b2g2f2=e2 | f4 F4 :: f2 f4 df | 
 g2 e4 de | e2 c4 de | fedc BAGF | E2 g4 fe | d2 f4 ed | e2c2B2A2 | B4 B,4 :|  