I would like to make a hierarchy of courses under the subject of math, it would look something like this

Mathematic

- Numbers

Fractions

- Comparing fractions (Here goes all activities, quizes and so on)

- Adding fraction

...

- Algebra

Equations

...

- Geometry

Volume

...

I looked at metacourse but I could only do one level and it's not enough. Do I have to create separate courses to accomplish this?