Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/8
M:4/4
K:Bb
['fe d2 B4', 'f2 fe .d(BAB) .d(BAB) .G(EDE) .G(EDE) cded']  
X:1
L:1/8
M:4/4
K:Bb
 fe | d2 B4 dB | cBAG F2 FE | DFBF GecA | B2 B2 B2 fe | d2 B4 gf | =e2 c4 cB | Acfa dbg=e | 
 f2 f2 f2 :: fe | .d(BAB) .d(BAB) | .G(EDE) .G(EDE) | cded edcB | BAcA F2 fg | .f(BAB) .g(BAB) | 
 .a(BAB) .b(BAB) | GBce dBcA | B2 B2 B2 :|  