By default the IntelliGantt Web Part will display a containment hiearchy based on folders and nested items.
To create 'Choice Folders' edit any SharePoint list view and add one or two choice columns to the 'Group By' section.
When the IntelliGantt Web Part finds a view with 'Group By' fields set, it will create virtual folders to match the choice values as necessary.
You can use the task manipulation window to create new tasks within a virtual folder.
The IntelliGantt Web Part will identify which choice fields are active for a virtual folder and add those values to your new task item.