How to solve exception thrown in traversing forest - c

Question

Question: Compute numbers of leaves in forest. Promblem: After debugging and printing a part of data, when I traverse printf("%d ", node->data);, incurred in a runtime error, that is, exception thrown: read access violation.
MainFunc.c
#include "AllFun.h"
int main(int argc, char* argv[])
{
CsNode* tree = (CsNode*)malloc(sizeof(CsNode));
if (tree) {
tree->firstchild = NULL;
tree->nextsibling = NULL;
CreateTree(&tree);
preOrder(tree);
int leaves = CountForestLeaves(tree);
printf("leaves: %d", leaves);
}
return 0;
}
AllFun.h
#include <stdio.h>
#include <stdlib.h>
typedef struct CsNode {
struct CsNode* firstchild;
struct CsNode* nextsibling;
int data;
}CsNode;
void CreateTree(CsNode** node);
void preOrder(CsNode* node);
int CountForestLeaves(CsNode* tree);
OtheFunc.c
#include "AllFun.h"
void CreateTree(CsNode** node)
{
int data;
printf("please input data: ");
scanf_s("%d", &data);
if (data != -1) {
*node = (CsNode*)malloc(sizeof(CsNode));
(*node)->data = data;
(*node)->firstchild = NULL;
(*node)->nextsibling = NULL;
CreateTree(&(*node)->firstchild);
CreateTree(&(*node)->nextsibling);
}
}
void preOrder(CsNode* node)
{
if (node != NULL) {
printf("%d ", node->data);
preOrder(node->firstchild);
preOrder(node->nextsibling);
}
}
int CountForestLeaves(CsNode* tree)
{
if (tree == NULL)
return 0;
if (tree->firstchild == NULL)
return 1 + CountForestLeaves(tree->nextsibling);
else {
return CountForestLeaves(tree->firstchild) + CountForestLeaves(tree->nextsibling);
}
}