Develop a musical piece incorporating the designated alphabet-based pattern and the supplied melodic theme.
X:1
L:1/8
M:6/8
K:Dmix
['F2 D DAG A3 GEA DED FED', 'DAG c2 A AGF G3 DGG Add']  
X:1
L:1/8
M:6/8
K:Dmix
|: F2 D DAG | A3 GEA | DED FED | GEA DAG | F3 G3 | A3 cde | dcA GEA | D3 DAG :: c2 A AGF | G3 DGG | 
 Add cAG | Ad^d =d2 e | fed cAG | FAF GEA | dcA GEA | D3 D2 B :|  