Develop a musical piece incorporating the designated alphabet-based pattern and the supplied melodic theme.
X:1
L:1/8
Q:1/2=100
M:2/2
K:C
['G2 GA', 'e2 ec']  
X:1
L:1/8
Q:1/2=100
M:2/2
K:C
 G2 GA GECE | F2 AG ABcA | G2 GA GEC z | fedc A2 c2 :: e2 ec f2 fd | e2 ec dBGB | e2 ec f2 fd | 
 gedc A2 c2 :|  