#include

using namespace std;

struct BSTnode $\{$

int data;

BSTnode $*$left;

BSTnode $*$right;

$\}$;

BSTnode $*$addNode$($BSTnode $*$root$,$ int value$)\{$

if $($root $==$ nullptr$)\{$

root $=$ new BSTnode;

root$->$left $=$ nullptr;

root$->$right $=$ nullptr;

root$->$data $=$ value;

return root;

$\}$ else if $($value $<$ root$->$data$)\{$

root$->$left $=$ addNode$($root$->$left, value$)$;

return root;

$\}$ else if $($value $>$ root$->$data$)\{$

root$->$right $=$ addNode$($root$->$right, value$)$;

return root;

$\}$

return root;

$\}$

int main$()\{$

BSTnode $*$root $=$ nullptr;

root $=$ addNode$($root$,1)$;

root $=$ addNode$($root$,3)$;

root $=$ addNode$($root$,5)$;

root $=$ addNode$($root$,8)$;

root $=$ addNode$($root$,-11)$;

root $=$ addNode$($root$,-15)$;

root $=$ addNode$($root$,-10)$;

$\}$

Provided a Binary Tree with each node with an integer value, write a function called average that will find the average of all of the leaf nodes in a Binary Tree. Remember, leaves are nodes that do not have any children. Feel free to define helper functions to help you with this task. write in C$++$ please.