https://github.com/staudenmeir/laravel-adjacency-list
https://laraveldaily.com/eloquent-recursive-hasmany-relationship-with-unlimited-subcategories/
https://www.gloomaps.com/
http://stackabuse.com/modified-preorder-tree-traversal-in-django/
https://pypi.python.org/pypi/django-treebeard
http://www.jstree.com/
http://be.twixt.us/jquery/treeView.php
http://dev.mysql.com/tech-resources/articles/hierarchical-data.html
http://www.evolt.org/article/Four_ways_to_work_with_hierarchical_data/17/4047/index.html