Develop a musical piece incorporating the designated alphabet-based pattern and the supplied melodic theme.
X:1
L:1/8
M:6/8
K:G
['GDG GDG', 'Bcd ded ded']  
X:1
L:1/8
M:6/8
K:G
 GDG GDG | GDG Bcd | GDG GDG | ABG FED | GDG GDG | GDG Bcd | efg dcB | ABG FED :: Bcd ded | 
 ded dcB | cde efe | efe edc | Bcd ded | ded def | gfe dcB | ABG FED :|  