print binary tree level by level in python

Here's my attempt, using recursion, and keeping track of the size of each node and the size of children.

class BstNode:

    def __init__(self, key):
        self.key = key
        self.right = None
        self.left = None

    def insert(self, key):
        if self.key == key:
            return
        elif self.key < key:
            if self.right is None:
                self.right = BstNode(key)
            else:
                self.right.insert(key)
        else: # self.key > key
            if self.left is None:
                self.left = BstNode(key)
            else:
                self.left.insert(key)

    def display(self):
        lines, *_ = self._display_aux()
        for line in lines:
            print(line)

    def _display_aux(self):
        """Returns list of strings, width, height, and horizontal coordinate of the root."""
        # No child.
        if self.right is None and self.left is None:
            line = '%s' % self.key
            width = len(line)
            height = 1
            middle = width // 2
            return [line], width, height, middle

        # Only left child.
        if self.right is None:
            lines, n, p, x = self.left._display_aux()
            s = '%s' % self.key
            u = len(s)
            first_line = (x + 1) * ' ' + (n - x - 1) * '_' + s
            second_line = x * ' ' + '/' + (n - x - 1 + u) * ' '
            shifted_lines = [line + u * ' ' for line in lines]
            return [first_line, second_line] + shifted_lines, n + u, p + 2, n + u // 2

        # Only right child.
        if self.left is None:
            lines, n, p, x = self.right._display_aux()
            s = '%s' % self.key
            u = len(s)
            first_line = s + x * '_' + (n - x) * ' '
            second_line = (u + x) * ' ' + '\\' + (n - x - 1) * ' '
            shifted_lines = [u * ' ' + line for line in lines]
            return [first_line, second_line] + shifted_lines, n + u, p + 2, u // 2

        # Two children.
        left, n, p, x = self.left._display_aux()
        right, m, q, y = self.right._display_aux()
        s = '%s' % self.key
        u = len(s)
        first_line = (x + 1) * ' ' + (n - x - 1) * '_' + s + y * '_' + (m - y) * ' '
        second_line = x * ' ' + '/' + (n - x - 1 + u + y) * ' ' + '\\' + (m - y - 1) * ' '
        if p < q:
            left += [n * ' '] * (q - p)
        elif q < p:
            right += [m * ' '] * (p - q)
        zipped_lines = zip(left, right)
        lines = [first_line, second_line] + [a + u * ' ' + b for a, b in zipped_lines]
        return lines, n + m + u, max(p, q) + 2, n + u // 2


import random

b = BstNode(50)
for _ in range(50):
    b.insert(random.randint(0, 100))
b.display()

Example output:

                              __50_________________________________________ 
                             /                                             \
    ________________________43_                   ________________________99
   /                           \                 /                          
  _9_                         48    ____________67_____________________     
 /   \                             /                                   \    
 3  11_________                   54___                         ______96_   
/ \            \                       \                       /         \  
0 8       ____26___________           61___           ________88___     97  
         /                 \         /     \         /             \        
        14_             __42        56    64_       75_____       92_       
       /   \           /                 /   \     /       \     /   \      
      13  16_         33_               63  65_   72      81_   90  94      
             \       /   \                     \         /   \              
            25    __31  41                    66        80  87              
                 /                                     /                    
                28_                                   76                    
                   \                                                        
                  29                                                        

class Node(object):
    def __init__(self, value, left=None, right=None):
        self.value = value
        self.left = left
        self.right = right
    
def printTree(node, level=0):
    if node != None:
        printTree(node.left, level + 1)
        print(' ' * 4 * level + '-> ' + node.value)
        printTree(node.right, level + 1)

t = Node(1, Node(2, Node(4, Node(7)),Node(9)), Node(3, Node(5), Node(6)))
printTree(t)

output:

            -> 7
        -> 4
    -> 2
        -> 9
-> 1
        -> 5
    -> 3
        -> 6