Craft a musical work based on the specified structure and given theme.
X:1
L:1/8
M:2/4
K:Bb
['.B2 gf edcB']  
X:1
L:1/8
M:2/4
K:Bb
 F2 | .B2 gf edcB | ABcd eFAB | BABA dced | fgec BAGF | .B2 gf edcB | ABcB AGFE | DBEB FBGB | 
 AgfA B2 :|  