title: Tree menu in Symfony 2, in one entity
body: <p>I'm using Symfony 2.3 framework.</p>
  
  <p>I am trying to create a system that will allow me to easily create tree menu (with root and child).</p>
  
  <p>This field allows to show whether it is a root or child (id of this entity another record).</p>
  
  <p>Now I want to do something like relation OneToMany but I don't know how. It is possibility to create relation with this same entity?</p>
  
  <p>I thing about create method 'getChildren' in this entity but I don't know what operation I should to do.</p>
  
  <p>Example:</p>
  
  <h2>class site { private $id; private $name; private $parent; }</h2>
  
  <p>and records in db:
  1 category_1 0
  2 subcategory_1 1
  3 subcategory_2 1
  etc.</p>