cs50 pset5 unload problem - memory leakage - c

Question

I am trying to solve the cs50 pset5. I am using a tries method.
I can insert word into the tries successfully. However, when i unload the memory, it fails. I am so stuck at the unload problem for a few days.
When I try the unload function, it stated that Erorr Message: double free or corruption (!prev): 0x000000000205d010 ***
It is probably due to my unload function, but i have drawn out the logic. It seems fine to me. Anyone has any idea where to amend?
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <string.h>
#include <ctype.h>
#define LENGTH 45
#define SIZE_OF_CHILD 27
typedef struct Node {
bool is_word;
struct Node* child[SIZE_OF_CHILD];
} Node;
Node* root;
Node* temp;
Node* create_node(Node* node);
void test();
int cal_key(char c);
Node* insert(const char* word);
void unload(Node* node);
int main() {
root = malloc(sizeof(Node));
if (root == NULL) {
exit(0);
}
root = create_node(root);
temp = malloc(sizeof(Node));
if (temp == NULL) {
exit(0);
}
test();
}
// **************** function to create a node *******************
Node* create_node(Node* node) {
node->is_word = false;
for (int i = 0; i < SIZE_OF_CHILD; i++) {
node->child[i] = NULL;
}
return node;
}
//************* calculate the key value ************
// Assume that the input is in lower case
int cal_key(char c) {
if (isalpha(c)) {
if (islower(c)) {
return c - 'a';
}
else {
return c + 32 -'a';
}
}
else {
return SIZE_OF_CHILD - 1;
}
}
//*************** function to insert an item in the the node ***********
Node* insert(const char* word) {
int str_len = strlen(word);
temp = root;
int key;
for (int i = 0; i < str_len; i++) {
key = cal_key(word[i]);
if (temp->child[key] == NULL) {
Node* node = malloc(sizeof(Node));
if (node == NULL) {
fprintf(stderr, "Error in creating node\n");
exit(0);
}
node = create_node(node);
temp->child[key] = node;
}
temp = temp->child[key];
}
temp->is_word = true;
return root;
}
//***************** function to unload a function ********************
void unload(Node* node) {
// This is to find the last node
for (int i = 0; i < SIZE_OF_CHILD; i++) {
if (node->child[i] != NULL) {
unload(node->child[i]);
}
free(node);
}
}
void test() {
root = insert("Peter");
unload(root);
}