C++ Implementation of Splay Tree

So I was to implement Splay function after inserting a new tree. However, when I tried to insert multiple ints it says Segmentation Fault (core dump) then exit.

Can anyone check where my problem is?

void SplayTree::splay(Node* node)
{
    if (node == NULL)

        return;
   while (node!=NULL) {
            Node* parent = node->parent;
            if (parent != NULL) {
                if (parent->left == node) {
                    rightRotate(parent);
                } else {
                    leftRotate(parent);
                }
            } else {
                Node* gparent = parent->parent;
                if (parent->left == node && gparent->left == parent) {
                    rightRotate(gparent);
                    rightRotate(node->parent);
                } else if (parent->right == node &&
                        gparent->right == parent) {
                    leftRotate(gparent);
                    leftRotate(node->parent);
                } else if (parent->left == node &&
                        gparent->right == parent) {
                    rightRotate(parent);
                    leftRotate(node->parent);
                } else {
                    leftRotate(parent);
                    rightRotate(node->parent);
                }
            }
        }

}

On line 15, you have essentially the following sequence of code:

 if (parent != NULL) {
        ...

  } else {
         Node* gparent = parent->parent;

So essentially you are checking if the parent is not NULL, then if it is NULL you immediately deference it (parent->parent), you are essentially doing this:

Node* parent = NULL; *parent;

Which is UB, and very likely to cause a segfault.

There are also a series of other deferenced parents so i think you will need to rethink how your function works.