php recursive function doesn't go into itself - php

Question

I wrote a recursive function in order to echo a nested list. In fact it's a helper function in laravel that get a collection of nested items and supposed to go through it and print all items' name.
But when I using it in view, just the first level of items is printed.
It seems to doesn't execute itself at items_list($item->children());.
function items_list($items)
{
foreach($items as $item) {
if(!$item->hasChild())
{
echo "
<li>
".$item->id.".".$item->name."
</li>
";
return null;
}
else
{
echo "<li>".
$item->id.".".$item->name
."<ul>";
items_list($item->children());
echo "</ul></li>";
}
}
}
here is the collection of items:
| id | parent_id | name |
+----+-----------+---------------------+
| 1 | NULL | Dr. Shany Braun Jr. |
| 2 | NULL | Lily Jerde |
| 3 | NULL | Dr. Herbert Kunze |
| 4 | 1 | Ms. Shanie Skiles |
| 5 | 1 | Dr. Anissa Kunze |
| 6 | 2 | Maybelle Sawayn |
| 7 | 3 | Cassie Trantow Jr. |
| 8 | 5 | Gussie Smith |
| 9 | 5 | Carol Mueller |
| 10 | 7 | Shany Bayer |
+----+-----------+---------------------+
edit:
The input of function is in fact a collection of an eloquent model that has retrieved from database I have printed above.
And here is the model:
class Person extends Model
{
protected $table = 'people';
function parent()
{
return $this->belongsTo(self::class, 'parent_id');
}
function children()
{
return $this->hasMany(self::class,'parent_id');
}
static function first_level()
{
return self::all()->where('parent_id', NULL);
}
function hasChild()
{
return ($this->children() ? TRUE : FALSE);
}
}
I have tested each function of this class and they work ‌properly.
and here is controller:
class HomeController extends Controller
{
public function show(){
$people = Person::first_level();
items_list($people);
}
}
and this is the output:
1.Dr. Shany Braun Jr.
2.Lily Jerde
3.Dr. Herbert Kunze