Item group and sub-group:-

Steps:-
1.Search Item-group in search bar.
2.Click on New.
3.Fill all required fields.
4.Click on save.

For example:

1. Material Testing
   1.1 Soil
   1.2 Brick
   1.3 Concrete
2. Design
   2.1 Architectural
   2.2 Structural
3. Surveying

Material Testing, Design and Surveying are Item Groups.
Soil, Brick and Concrete are the sub groups of Material Testing.