code: def max_branch_sum(node):
      if node is None:
          return 0
  
      # take the max left subbranch sum and add the current node value
      left_max_sum = max_branch_sum(node.left) + node.val
      # take the max right subbranch sum and add the current node value
      right_max_sum = max_branch_sum(node.right) + node.val
  
      # return the bigger sum
      return max(left_max_sum, right_max_sum)
  
label_desc: Use image node_id 1 for calling a global function with example usage: max_branch_sum(node) and returns: max, int