PHP - 用于查找任何给定父级的父级的递归函数 - 问题

I hope somebody can help, this is driving me crazy!

I have a simply recursive PHP function for getting all parents to any given parent for a list of categories. You simply pass it the parent category ID for any given category and it will recursively get all the parents further up the tree.

function getParentCategoriesById($parent_category_id,array $parents = []){

if(empty($parent_category_id)) {
    return [];
}

$parents[] = $parent_category_id;

$parent_category = DB::builder()->table('product_categories')->find($parent_category_id);

if(!empty($parent_category->parent)) {
    getParentCategoriesById($parent_category->parent,$parents);
}

return $parents;}

Let's say category id=100 has 2 parents (33->37), if I dump the $parents array just before the return, the results are:

Array
(
    [0] => 33
    [1] => 37
)

Array
(
    [0] => 33
)

The first array returned is the correct result, but I don't understand how the function is re-running and then instead returning only the first parent.