binary tree traversal code explaination needed [closed]

Question

I have a question on how this binary tree traversal code works.

void BinaryTree_Functions::preorder(Binary_TreeNode* bt)
    {
        if (bt == NULL) { return; }
        cout <<  bt->data <<endl;
        preorder(bt->Left);
        preorder(bt->Right);
    }

preorder traversal

    void BinaryTree_Functions::inorder(Binary_TreeNode* bt)
    {
        if (bt == NULL) { return; }
        inorder(bt->Left);
        cout << bt->data << endl;
        inorder(bt->Right);
    }

inorder traversal

    void BinaryTree_Functions::postorder(Binary_TreeNode* bt)
    {
        if (bt == NULL) { return; }
        postorder(bt->Left);
        postorder(bt->Right);
        cout << bt->data << endl;
    }

postorder traversal

I know how these traversals work but I did not understand the code.