* [ ] `HierarchicalItemService`
* [x] `initialize(custom_field)`
* [x] DryValidation for custom field (type)
* [x] `generate_root`
* [x] `insert_item(parent, label, short = nil)`
* [x] DryValidation (ifChild?, labelSet?)
* Begin of the insertion[x]End of the insertion Begin of the deletion [ ]End of the deletion `delete_branch(item || item_id)`
* [ ] `soft_delete_branch(item || item_id)`
* Begin of the insertion[x]End of the insertion Begin of the deletion [ ]End of the deletion `update_item(item, label, short)`
* [ ] `move_item(item, parent, sort_order)`
* [ ] `get_branch(item)` -> Item\[\]