Develop a musical piece using the given theme and incorporating the letter-based structure provided.
X:1
L:1/8
M:4/4
K:G
['Bc dBcA', 'dg g2 bg g2 dgbg edBG FGAB', 'BDGB dgfg ec c2 Gceg fd d2']  
X:1
L:1/8
M:4/4
K:G
|: Bc | dBcA BGAF | DGGF GABc | dg g2 bgdB | cAAG A2 Bc | dBcA (3Bcd AF | DGGF GABc | 
 dgfg (3efg af | g2 gf g2 :: Bc | dg g2 bg g2 | dgbg edBG | FGAB cBcf | afge dcBc | dg g2 bg g2 | 
 dgbg edBG | FGAB cDFA | BGGF G2 :: dc | BDGB dgfg | ec c2 Gceg | fd d2 fgaf | gfga bgdc | 
 BDGB dgfg | ec c2 Gceg | fd d2 fgaf | gb (3agf g2 :|  