How to create a new tag that is a subtag of another tag ?

In DTTG, how does one create/add a tag that is a sub-tag of another tag. For example, I have the tag “2018”. I want to create a tag “January” that will be a child to “2018”, as in 2018 > January. A hierarchy or tags can be created in the desktop app, but does one do this in iOS?

This is currently not supported in DTTG2. It may be part of a future release.