Develop a musical piece incorporating the designated alphabet-based pattern and the supplied melodic theme.
X:1
L:1/8
M:2/4
K:G
['Bd ed dB GA Bd eg ba', 'ab Bd']  
X:1
L:1/8
M:2/4
K:G
|: Bd ed | dB GA | Bd eg | ba a2 | ag/a/ ba | gb eg | Bd e/f/g |1 BG GA :|2 BG gf |: e>f ed | 
 eg ab | Bd ed | BG A2 | e>f ed | e/f/g ab | Bd e/f/g |1 BG gf :|2 BG GA ||  