Tidak mau insert ke phpmyadmin

Kenapa ya kak? Padahala Sudah Tepat semua yang mau di insert tapi kenapa masih gak nge-insert juga ya?

<?php
include "config/koneksi.php";

$a = $_POST['nama'];
$b = $_POST['username'];
$c = $_POST['password'];
$d = Member;
$e = $_POST['nomor'];
$f = $_POST['alamat'];
$g = $_POST['email'];
$h = $_POST['facebook'];
$i = $_POST['instagram'];
$j = Suspend;
$k = $date;

if (empty($a)) {
  echo "<script>window.alert('Nama Belum diisi')
  window.location='daftar.php'</script>";

} else if (empty($b)) {
  echo "<script>window.alert('Username Belum diisi')
  window.location='daftar.php'</script>";

} else if (empty($c)) {
  echo "<script>window.alert('Password Belum diisi')
  window.location='daftar.php'</script>";

} else if (empty($e)) {
  echo "<script>window.alert('Nomor Belum diisi')
  window.location='daftar.php'</script>";

} else if (empty($f)) {
  echo "<script>window.alert('Alamat Belum diisi')
  window.location='daftar.php'</script>";

} else if (empty($g)) {
  echo "<script>window.alert('Email Belum diisi')
  window.location='daftar.php'</script>";

} else if (empty($h)) {
  echo "<script>window.alert('Url Facebook Belum diisi')
  window.location='daftar.php'</script>";

} else if (empty($f)) {
  echo "<script>window.alert('Url Instagram Belum diisi')
  window.location='daftar.php'</script>";

} else {
        session_start();
  $check_user = mysqli_query($conn, "SELECT * FROM member WHERE username='$b'");
	$data_user = mysqli_fetch_assoc($check_user);
   if (mysqli_num_rows($check_user) > 0)
      echo "<script>window.alert('Username telah terpakai')
  window.location='daftar.php'</script>";
 } if (strlen($c) < 5) {
  echo "<script>window.alert('Password minimal 5 karakter.')
  window.location='daftar.php'</script>";


$insert_user = mysqli_query($conn, "INSERT INTO member (nama,username,password,level,nomor,alamat,email,facebook,instagram,status,time) VALUES ('$a','$b','$c','Member','$e','$f','$g','$h','$f','Error','$date')");
   } if ($insert_user == true) {
 echo "<script>window.alert('Berhasil, user berhasil ditambahkan. Untuk Aktivasi silahkan hubungi Pengurus')
  window.location='index.php'</script>";
   } if ($insert_user == false) {
       echo "<script>window.alert('Gagal')
  window.location='daftar.php'</script>";
   } if ($insert_user == true) {
 echo "<script>window.alert('Berhasil, user berhasil ditambahkan. Untuk Aktivasi silahkan hubungi Pengurus')
  window.location='index.php'</script>";

}

?>