Step 1: Add Options

Add options of custom field in admin panel (Settings → App → MLCS Cloud):

Step 2: Create custom field for your issues

Now you need create a custom field for issues, follow steps:

1) Go to Settings → issues

2) Go to Custom field → click on create custom field

3) Find MLCS (Advanced → Multi Level Cascading)

4) Set a name

5) Select all screens and context where you need custom field

6) MLCS now are available on any issue

Step 3: Multi-tree

You can set root of tree to single or any custom field type you have created: