Undefined property when accessing model class

[eluser]Unknown[/eluser]
hi, please help me with this problem

Code:

class Test extends Controller
{

    function Test()
    {
        parent::Controller();
    }
    
    function index()
    {
        $this->load->model('category_model');
        $this->category_model->get(1);
    }
}

class Category_model extends Model
{
    function Category_model()
    {
        parent::Model();
    }
  
    function get($id)
    {
        // some function to get data from database
    }
}

Code:

A PHP Error was encountered

Severity: Notice

Message: Undefined property: Test::$category_model

Filename: controllers/test.php

Line Number: 16