def find(self,key):
        if self.size == 0:
            raise NotFoundException
        else:
            value = MyComparableKey(key,None)
            node = self._recur(value,self.root)
            if node != None:
                return node.root.string_value
            else:
                raise NotFoundException

    def _recur(self,value,node):
        if node == None:
            return node
        elif node.root < value:
            self._recur(value,node.right)
        elif value < node.root:
            self._recur(value,node.left)
        else:
            return node