Develop a musical piece incorporating the designated alphabet-based pattern and the supplied melodic theme.
X:1
L:1/8
M:4/4
K:D
['FG Adfd Adfd Adge B2 ed cdec', 'FG A2 f2 fgfe B2 g2 g3']  
X:1
L:1/8
M:4/4
K:D
 FG | Adfd Adfd | Adge B2 ed | cdec A2 Bc | defd A2 FG | Adfd Adfd | Adge B2 ed | cdec AABc | 
 d2 f2 d2 :| FG | A2 f2 fgfe | B2 g2 g3 e | cdec A2 Bc | defd A2 FG | A2 f2 fgfe | B2 g2 g3 e | 
 cdec AABc | d2 f2 d2 :|  