When to use delete to free the memory allocated by new

I am learning cpp. I was learning how to insert elements in bst and got confused on when to use "delete" to free the memory allocated by new:

Here is my program

    Node * insert(Node * root, int data) {
        Node * temp;
        Node * prev;
        Node * newnode = new Node(data);
        if(root == nullptr)
        {
            root = newnode;
        }
        else
        {
            temp = root;
            while(temp!=NULL/*temp->left != NULL || temp->right!=NULL*/ )
            {
                prev = temp;
                if(newnode->data > temp->data)
                {
                    temp = temp->right;

                }
                else
                {
                    temp = temp->left;

                }

            }
            if(prev->data > newnode->data){prev->left = newnode;}
            else
            {
                prev->right = newnode;
            }

        }

        **//delete newnode**;(if I use delete , root becomes dangling (if I guess correctly) and program crashes)
        cout<<"returning root "<<root->data;
        return root;
    }
};

The Node class definition is

class Node {
    public:
        int data;
        Node *left;
        Node *right;
        Node(int d) {
            data = d;
            left = NULL;
            right = NULL;
        }
};

If I dont use delete, program works fine but I understand it causes memory leak and want to learn to avoid that in such scenarios Thank you in advance.