Develop a musical piece incorporating the designated alphabet-based pattern and the supplied melodic theme.
X:1
L:1/8
M:6/8
K:Bb
['D2 D']  
X:1
L:1/8
M:6/8
K:Bb
 z D | G3/2 ^F/ G B2 B | (G^F) =E D2 D | d2 d BA G | (A3 A2) d | d2 d B A G | G ^F G D2 D | 
 (GA) B (cA) B | (G3 G2) x |]  