PHP unlimited classification and tree

PS： I don't know how to traverse the tree without limit , I feel that it is only suitable for defining the total number of layers , For example, one 、 Two 、 Three level menu , Not suitable for infinite

Infinite classification （ Recursive method ）：

/*
 Recursive infinite classification 
 */
function unlimitedMenu($arr,$pid=0,$level=0){
	static $list = array();
	foreach ($arr as $v) {
		// If it's a top-level category , Then save it to $list in , And take this node as the root node , Traversing its child nodes 
		if ($v['pid'] == $pid) {
			$v['level'] = $level;
			$list[] = $v;
			unlimitedMenu($arr,$v['id'],$level+1);
		}
	}
	return $list;
}

Tree menu （ One ）：

/*
 The array returns a tree structure 
$id  Self increasing ID Field name 
$pid  Parent class id Field name 
$son  Key name of subset 
 */
function tree($array,$id='id',$pid='pid',$son='son'){
    $temp = [];
    foreach ($array as $v) {
        $v[$son] = [];
        $temp[$v[$id]] = $v;
    }
    // Get classification tree 
    foreach ($temp as $k => $v) {
        $temp[$v[$pid]][$son][] = &$temp[$v[$id]];
    }
    return isset($temp[0][$son]) ? $temp[0][$son] : [];
}

Tree menu （ Two ）：

function getChild($data, $id = 0)
{
	// Initialize son 
	$child = [];
	// Cycle all data to find $id Son 
	foreach ($data as $key => $datum) {
		// I found my son 
		if ($datum['pid'] == $id) {
			// preserved , Then continue to find his son's son 
			$child[$datum['id']] = $datum;
			// Get rid of yourself first , You can't be your own grandchildren 
			unset($data[$key]);
			// Recursively look for , And put the found son in a child In the field of 
			$child[$datum['id']]['child'] = getChild($data, $datum['id']);
		}
	}
	return $child;
}