Some modules display a taxonomy field in a tree (Taxonomy Term Reference Tree). At the time of this writing, however, it does not work.
Making a taxonomy tree is easy.. so we will do it ourself.
We first create a taxonomy view of the terms.
We provide a content type where we can make the necessary choices in the field. The default display of the field shows only the last part of this term (child)
We will solve this and make something like that: (notice this is a node with a selection of the terms)
We create a view where we set the relationships with the parent terms
And make it mandatory. The parents themselves without a parent are not displayed!
We place the parents as a field.
And group on it ... If you set a group, you have to set the field invisible.
We are going to link it to a node through a contextual filter to the node ID. So you see here that I call node 30 ...
Finally, we make an EVA (EVA module) to link it to the display in the content type.