Develop a musical piece incorporating the designated alphabet-based pattern and the supplied melodic theme.
X:1
L:1/8
M:3/4
K:Bb
['FA B2 AG AB c4 cdecdB cc']  
X:1
L:1/8
M:3/4
K:Bb
 FA B2 AG | AB c4 | cdecdB | cc B4 | d>e f2 d2 | cd e2 c2 | d>e f2 d2 | cd e2 c2 | FA B2 AG | 
 AB c4 | cdecdB | cc B4 |]  