Can't see option hierarchy when creating a vocabulary

If I crea开发者_JAVA百科te a Taxonomy (vocabulary), I can't see the option hierarchy, what can be the reason of that?

This option have been removed in 6.

Every vocabulary can be hierarchical. If you want to add a child term, just drag it to the right, it will become a child.

It's possible that you have this vocabulary selected as a "free-tagging" type of vocabulary. In that case, hierarchy is not relevant. I had a client who discovered that his hierarchy for a vocabulary had disappeared. The reason for this was that he'd changed that vocabulary to the free tagging type.

You access this by going to Content > Taxonomy to edit the vocabulary in question.