C :: Write / Read Tree Nodes Into A Binary File

I have a binary tree, and I want to store all information its leaves stores into a binary file and then read it.

What I tried:

A function that reads the tree, and whenever it finds a leaf, it writes in the binary file:

Code:
[...]
if(tree->right == NULL && tree->left == NULL){
fwrite(tree, sizeof(tree), 1, output);
}
[...] a

And in the main function:

Code:
[...]
for(i=0;i<5;i++){
fread(tree, sizeof(tree), 1, output);
printf("This is the leaf number %d", tree->num);
}
[...]

I'm trying to read 5 nodes just to see if its working but it isn't. The output shows the first node of the tree everytime.