Develop a musical piece using the given theme and incorporating the letter-based structure provided.
X:1
L:1/8
Q:1/4=140
M:4/4
K:Bb
['D E F2 F D F B', 'c B']  
X:1
L:1/8
Q:1/4=140
M:4/4
K:Bb
 D E | F2 F D F B | d2 B2 F d | c2 A F A c | B2- B z :| c B | A2 A c B G | G2 F2 c B | A2 A c B G | 
 F2- F z D E | F2 F D F B | d2 B2 F d | c2 A F A c | B4 ||  