C++

Why am I getting a segmentation fault: 11?

int main()

{

BinarySearchTree tree;

NodeType *T;

T = tree.insert(10,T);

tree.preOrderPrint(T);

}

***********************************

struct NodeType {

int key;

NodeType *lptr;

NodeType *rptr;

};

class BinarySearchTree{

public:

BinarySearchTree();

NodeType* insert(const int&, NodeType*);

void preOrderPrint(NodeType *root);

private:

NodeType* root;

};

BinarySearchTree::BinarySearchTree(){

root = NULL;

}

NodeType* BinarySearchTree::insert(const int& x, NodeType *root){

NodeType *n = new NodeType;

n->key = x;

n->lptr = n->rptr = NULL;

if(root == NULL)

root = n;

else {

NodeType *curr = root;

NodeType *prev;

while(curr != NULL) {

prev = curr;

if(x < curr->key)

curr = curr->lptr;

else

curr = curr->rptr;

}

if(x < prev->key)

prev->lptr = n;

else

prev->rptr = n;

}

return root;

}

void BinarySearchTree::preOrderPrint(NodeType *root) {

if(root!= NULL){

cout << root->key << endl;

preOrderPrint(root->lptr);

preOrderPrint(root->rptr);

}

}