recursive delete on a binary tree

Question

I am trying to understand how the recursive method of deletion of a binary search tree works. The code that I came across in many places looks as follows:

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Answer 1

It looks like this at that point:

void destroy_tree(struct node *leaf_5)
{
  if( leaf_5 != 0 )  // it's not
  {
      destroy_tree(leaf_5->left); // it's NULL so the call does nothing
      destroy_tree(leaf_5->right); // it's NULL so the call does nothing
      free( leaf_5 );  // free here
  }
}

Nothing is required to return... the "history" of the steps is on the call stack, which looks something like this at that point:

destroy_tree(leaf_10)
  destroy_tree(leaf_10->left, which is leaf_6)
    destroy_tree(leaf_6->left, which is leaf_5)

So after leaf_5 is gone, it goes back up the stack and does destroy_tree(leaf_6->right, which is leaf_8)... etc...