Bagaimana cara Membuat multiple insert di Codeigniter

Assalamualaikum Warahmatullahi Wabarakatuh...
Mohon bantuannya untuk membuat input 1 form ke dalam 2 table 
 
controller
 public function add()
    {
        $job = $this->M_kanban;
        $validation = $this->form_validation;
        $validation->set_rules($job->rules());
 
        if ($validation->run()) {
            $job->save_plan();
 
            $this->session->set_flashdata('success', 'Berhasil disimpan');
        }
 
        $product = $this->M_product;
        $data["product"] = $product->getAll();
        if (!$data["product"]) show_404();
 
        $this->load->view("base/kanban/add_job", $data);
    }
 
 
Model
public function save_plan()
		{	
			$post = $this->input->post();
			$product = $this->input->post('product');
			$this->db->trans_start();
			//INSERT TO PACKAGE
			date_default_timezone_set("Asia/Bangkok");
			$data  = array(
				'nm_customer' => $post["nm_customer"],
				'product_id' => $post["product_id"],
				'qty' => $post["qty"],
				'created_at' => date('Y-m-d H:i:s'), 
				'status' => $post["status"]				
			);
			$this->db->insert('job', $data);
			//GET ID PACKAGE
			$job_id = $this->db->insert_id();
			$result = array();
				foreach ($product as $key => $val) {
					$result[] = array(
					'job_id'  	=> $job_id,
					'days'		=> $val
					);
 
				}
			//MULTIPLE INSERT TO DETAIL TABLE
			$this->db->insert('plan_job', $result);
			$this->db->trans_complete();
		}
 
View
<div class="form-group">
                <label for="days">Days*</label>
                <select multiple class="form-control" name="product[]" data-width="100%" data-live-search="true" multiple required>
                  <option value="1">1</option>
                  <option value="2">2</option>
                  <option value="3">3</option>
                  <option value="4">4</option>
                  <option value="5">5</option>
            </select>
                <input class="form-control"
                 type="text" name="" min="0" placeholder="Days" />
              </div>