A
|_ DIR A1
|  |_ file_a1_1
|
|_ DIR A2
|  |_ file_a2_1
|
|_ file_a_1
|_ file_a_2
|_ a_file_not_duplicated

B
|_ DIR B1
|  |_ file_a1_1
|  |_ file_a_1
|
|_ DIR B2
|  |_ file_a2_1
|  |_ file_b_1   (<= only duplicated in B)
|  |_ file_b_2   (<= only duplicated in B)
|
|_ file_a_1
|_ file_a_2
|_ file_a1_1
|_ file_a2_1
|_ file_b_1
|_ file_b_2