Self related Category table (infinite nested array)

Dear phalcon community,

I need a help with this. I have a category table with such structure:

'id', 'name', 'parent_id'

The model:

class Category extends Model
{
public $id;
public $name;
public $parent_id;

public function initialize() {
$this->hasMany("id", 'Category', "parent_id", ['alias' => 'children']);
$this->belongsTo("parent_id", 'Category', "id", ['alias' => 'parent']);
}

public function getSource()
{
return 'category';
}

public function getCategories($parameters = null)
{
return $this->getRelated('children', $parameters);
}

}

I am trying to get all children of each of category in model with function getCategories. But unfortunately it shows error:

Model 'Category' could not be loaded

Can someone help me? How to make a self relation with parent_id?