PHP - Recursive binary tree -

i've been having fun php trying explore potentials tried see if can implement binary tree structure. here code:

class node{     public $leftnode;     public $rightnode;     public $value;     public function node($value){         $this->value = $value;     } }  class bintree{     public function inserter(node $node, $value){         if($value < $node->value){             if($node->leftnode != null){                 inserter($node, $value);             }             else{                 $node->leftnode = new node($value);             }         }         else if($value > $node->value){             if($node->rightnode != null){                 inserter($node, $value);             }             else{                 $node->rightnode = new node($value);             }         }     }    } 

now reason, when try call inserter function within (i.e. inserter ($node, $value), error: fatal error: call undefined function inserter(). tried referencing via $this , bintree:: no luck. fatal error: using $this when not in object context , fatal error: allowed memory size of 134217728 bytes exhausted errors respectively. can explain happening?

i suspect problem following:

php constructor works way

public function __construct () {  } 

(vs c# syntax using)