Create directory tree with one-liner:
for i in {a/{aa,ab,ac},b/{ba,bb,bc/{bca,bcb}},c}; do mkdir -p z/$i/{z1,z2}; done
Will produce below tree structure under directory z:
z/
|-a/
| |-aa/
| | |-z1/
| | |-z2/
| |
| |-ab/
| | |-z1/
| | |-z2/
| |
| |-ac/
| |-z1/
| |-z2/
|
|-b/
| |-ba/
| | |-z1/
| | |-z2/
| |
| |-bb/
| | |-z1/
| | |-z2/
| |
| |-bc/
| |-bca/
| | |-z1/
| | |-z2/
| |
| |-bcb/
| |-z1/
| |-z2/
|
|-c/
|-z1/
|-z2/