Return parents and childs from model

I have a model "Node". A node may have many childs and many parents.

So, the tables look like this

table nodes

id | name    | created_at | updated_at
1  | Node A  | ..         | ..
2  | Node B  | ..         | ..
3  | Node C  | ..         | ..
4  | Node D  | ..         | ..

table nodes_relations

id | nodes_id | relation_nodes_id | created_at | updated_at
1  | 2        | 1                 | ..         | ..
1  | 3        | 1                 | ..         | ..
1  | 4        | 2                 | ..         | ..

Briefly:

• Node A has 0 parents and 2 childs (node B and node C)
• Node B has 1 parent (node A) and 1 child (node D)
• Node C has 1 parent (node A) and 0 childs
• Node D has 1 parent (Node B) and 0 childs

In my Node class, I have defined the following relation:

    public function parents()
    {
        return $this->hasMany('App\NodesRelations','nodes_id');
    }

    public function children()
    {
        return $this->hasMany('App\NodesRelations', 'relation_nodes_id');
    }

And this is the class NodeRelation:

class NodesRelations extends Model
{
    //

    public function parent()
    {
        return $this->belongsTo('App\Nodes', 'relation_nodes_id');
    }

    public function self()
    {
        return $this->belongsTo('App\Nodes', 'nodes_id');
    }
}

I have a simple view to test the response:

$node = App\Nodes::with('parents','parents.self','children','children.self')->findOrFail($node_id);

echo $node;

The problem is that I do see the children with a the needed info (name for instance), when $node_id = 1, but parents is null when i query $node_id = 2.

Can somebody point me in the right direction? I have been struggling about this for hours now. Thanks in advance.