entity_reference_tree-8.x-1.x-dev/entity_reference_tree.services.yml

services:
  # Taxonomy tree builder
  entity_reference_taxonomy_term_tree_builder:
    class: Drupal\entity_reference_tree\Tree\TaxonomyTreeBuilder
    tags:
      - { name: entity_reference_tree_builder, priority: 1000 }
  # General entity builder    
  entity_reference_entity_tree_builder:
    class: Drupal\entity_reference_tree\Tree\EntityTreeBuilder
    tags:
      - { name: entity_reference_tree_builder, priority: 1000 }