Develop a musical composition using the outlined alphabetical depiction of the structure and the provided theme.
X:1
L:1/8
M:6/8
K:G
['G A_BGABG A_Bc d2 c _BABGAB G3']  
X:1
L:1/8
M:6/8
K:G
 G | A_BGABG | A_Bc d2 c | _BABGAB | G3 z2 d | d_edc_BA | _B3 A2 A | G2 GDEF | G2 z3 |]  