CodeIgniter form using base_url() in the action attribute carries no POST data [closed]

I can't insert data into my MySQL database. I am confused about where the code is flawed.

View: tambah_berita.php

<form name="form" action="<?php echo base_url();?>index.php/admin/berita/tambah_berita" method="post">
    <div class="two fields">
        <div class="field">
            <label>ID_Berita</label>
            <div class="ui small left icon input">
                <input type="text" placeholder="ID" name="id_berita">
                <i class="text file outline icon"></i>
            </div>
        </div>
    </div>

    <div class="fours fields">
        <div class="field">
            <div class="ui vertical segment">
                <div class="date field">
                    <label>Tanggal</label>
                    <div class="ui small icon input left">
                        <input type="text" placeholder="xx/xx/xxxx" name="tanggal">
                        <i class="calendar icon"></i>
                    </div>
                </div>
            </div>
        </div>
    </div>
    <div class="two fields">
        <div class="field">
             <label>Judul</label>
            <div class="ui small left icon input">
                <input type="text" placeholder="Nama Profil" name="judul_berita">
                <i class="text file outline icon"></i>
            </div>
        </div>
    </div>
    <div class="field">
        <label>Isi Berita</label>
        <textarea placeholder="Text" name="content"></textarea>
    </div>

    <input class="ui small blue submit button" name="submit" type="submit" value="Save">
    <input class="ui small basic button" type="reset" value="Reset">
</form>

and model mberita.php

function get_berita()
{   
    $this->db->order_by('id_berita', 'asc');
    $data = $this->db->get('berita_ukm');
    return $data->result();
}

//untuk menambah berita
function insert_berita($data)
{
    print_r($data);
    $this->db->insert('berita_ukm', $data);
}

and controller berita.php

function index()
{
    $this->data['berita'] = $this->mberita->get_berita();
    //var_dump($this->mberita->get_berita());
    $this->data['title'] ='UKM Taekwondo | berita';
    $this->data['orang'] = $this->mlogin->dataPengguna($this->session->userdata('username'));
    $this->data['contents'] = $this->load->view('admin/berita/view_berita', $this->data, true);
    $this->load->view('template/wrapper/admin/wrapper_ukm',$this->data);
}

function tambah_berita()
{   
    $this->form_validation->set_rules('id_berita', 'Id Berita', 'required|numeric');
    $this->form_validation->set_rules('tanggal', 'Tanggal', 'required');
    $this->form_validation->set_rules('judul_berita', 'Judul Berita', 'required');
    $this->form_validation->set_rules('content', 'Content', 'required');

    if ($this->form_validation->run() == false) {
        $this->data['contents'] = $this->load->view('admin/berita/tambah_berita', '', true);
    } else {
        $this->load->model('mberita');

        $data = array(
            'id_berita' => $this->input->post('id_berita'),
            'tanggal' => $this->input->post('tanggal'),
            'judul_berita' => $this->input->post('judul_berita'),
            'content' => $this->input->post('content')  
        );

        $this->mberita->insert_berita($data);
    }
        
    $this->data['orang'] = $this->mlogin->dataPengguna($this->session->userdata('username'));
    $this->load->view('template/wrapper/admin/wrapper_ukm', $this->data);
}