python - How do you get a minimum value from a binary search tree -

i have created binary search class struggling create minimum function find smallest value in binary tree.

class binarysearchtree:      def __init__(self, data):         self.data = data         self.left = none         self.right = none      def insert(self, new_data):         if new_data == self.data:             return         elif new_data < self.data:             if self.left == none:                 self.left = binarysearchtree(new_data)             else:                 self.left.insert(new_data)         else:             if self.right == none:               self.right = binarysearchtree(new_data)             else:                self.right.insert(new_data)      def create_string(self,spaces):         info = ' ' * spaces + str(self.data)         if self.left != none:             info += '\n(l)' + self.left.create_string(spaces + 4)         if not self.right == none:             info += '\n(r)' + self.right.create_string(spaces + 4)         return info      def __str__(self):         representation = self.create_string(0)         return representation      def get_left(self):         return self.left      def get_right(self):         return self.right      def get_data(self):         return self.data  def minimum(tree):     if tree.left:         return minimum(tree.get_left)     else:         return tree.get_left 

so wrote minimum function reason returns nonetype error. have idea how get_left on binary tree until there no more nodes

non-recursive solution

def minimum(tree):     while tree.left not none:         tree = tree.left     return tree.data