Develop a musical piece using the given theme and incorporating the letter-based structure provided.
X:1
L:1/8
Q:1/2=90
M:2/2
K:D
['A2 A2 F2 GA B2 B2 A4', 'd4 f2 f2 e2 dc d2 ed']  
X:1
L:1/8
Q:1/2=90
M:2/2
K:D
 A2 A2 F2 GA | B2 B2 A4 | Bc d2 cd e2 | fgfe d4 :: f2 f2 e2 dc | d2 ed c2 A2 | Bcde cdef | 
 defg e4 | A2 A2 F2 GA | B2 B2 A4 | Bc d2 cd e2 | fgfe d4 :|  