class TreeNode:
   def __init__(self, data, left = None, right = None):
      self.val = data
      self.left = left
      self.right = right
def print_tree(root):
   if root is not None:
      print_tree(root.left)
      print(root.val, end = ', ')
      print_tree(root.right)
class Solution:
   def solve(self, root):
      max_size = [0]
      max_node = [None]
      def traverse(node):
         if not node:
            return []
      left = traverse(node.left)
      right = traverse(node.right)
      lst = left + [node.val] + right
      if sorted(lst) == lst:
         if max_size[0] < len(lst):
            max_size[0] = len(lst)
            max_node[0] = node
      return lst

   traverse(root)
   return max_node[0]
ob = Solution()
root = TreeNode(12)
root.left = TreeNode(3)
root.right = TreeNode(5)
root.right.left = TreeNode(4)
root.right.right = TreeNode(6)
print_tree(ob.solve(root))

root = TreeNode(12)
root.left = TreeNode(3)
root.right = TreeNode(5)
root.right.left = TreeNode(4)
root.right.right = TreeNode(6)

4, 5, 6,