Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/16
M:2/4
K:Bb
['BFDF BdcB cAFA cedc dbfd g2fe', 'B4 BcBA BcBA Bcde f2F2 GAG^F GAG^F']  
X:1
L:1/16
M:2/4
K:Bb
|: BFDF BdcB | cAFA cedc | dbfd g2fe | d2cB A2GF | BFDF BdcB | cAFA cedc | dbfd g2fe | dcBA B4 :: 
 BcBA BcBA | Bcde f2F2 | GAG^F GAG^F | GABc d2D2 | EFED EFED | EFGA B2B,2 | C2g2 fdec | B2F2 B,4 :|  