SIGSEGV (Segmentation fault) c++ at fuction for pushBack() of list

I catched segfault when run this code and can`t understand why. If firstly i use one time push(&head,3); then segfault is not catched, but it works bad for true

#include <iostream>
using namespace std;
struct Node
{
    int data;
    Node *next;
};

void push(Node **head,int data)
{
    Node *tmp = new Node;
    tmp->data = data;
    tmp->next = (*head);
    (*head) = tmp;
}
Node *getLast(Node *head)
{
    if(head == nullptr)
    {
        return nullptr;
    }
    while(head->next)
    {
        head=head->next;
    }
    return head;
}
void show(const Node *head)
{
    while(head!=nullptr)
    {
        cout << head->data << endl;
        head = head->next;
    }
}

void pushBack(Node *head,int data)
{
    Node *last = getLast(head);
    Node *tmp = new Node;
    tmp->data = data;
    tmp->next = nullptr;
    last->next = tmp;
}
int main() {
    Node *head=nullptr;
    **//push(&head,2);  /////if I use this then it works! but it not right.**
    pushBack(head,10);
    pushBack(head,2);
    pushBack(head,3);
    show(head);
    return 0;
}

I tried to google it but it helpless. How to solve this problem?