Why do I need to define new Trienode in the following code as the new TrieNode(); when I do it as new TrieNode; it gives segmentation fault. Is there a default constructor for struct datatype that’s important to call here, if so what does it do?

    struct TrieNode 
    {
    struct TrieNode *children[ALPHABET_SIZE];
    bool isLeaf;
    };
    void insert(struct TrieNode *root, string key)
    {
        for(int i=0; i<key.size(); i++)
        {
            if(root->children[key[i]-'a'] ==NULL)   root->children[key[i]-'a'] = new TrieNode();
            root = root->children[key[i]-'a'];
        }
        root->isLeaf = true;
        
    }