C++ Data structure Tree

I could not find in my book or notes how to find the size of a node in a Tree. Would anyone be able to help me as to how to go about this procedure???

struct BTNode {
BTNode* right;
BTNode* left;
double data;
};

#include <iostream>
int main() {
BTNode temp;
std::cout << sizeof temp << endl;

char wait; cin >> wait;
return 0;
}

Thank you very much!