the Hierarchy Component is thought to display a nested list of elements coming from different entities connected by relationships.
The behaviour you described is correct, because in your case, the Hierarchy Component displays all the records in Titolario and then, it display a child element for those having one.
In this way children elements are displayed twice: once because they belong to the entity Titolario, and twice because they belong to the Level you defined on the Hierarchy.
If you want to obtain a proper result, you should use the Recursive Hierarchy Component, that allows to display a nested list of elements coming from the same entity and connected by a recursive relationship.
You can fine more details in the following online lesson: