wordpress add to database table

gistfile1.txt

/// HTML PAGE TEMPLATE SHOULD HAVE THIS CODE (KEEP IN MIND THAT THE INSERT.PHP IS IN THE TEMPLATE DIR

<form action="<?php echo get_template_directory_uri(); ?>/insert.php" method="post">
Name:<input type="text" name="name"/>
<input type="submit" name="submit"/>
</form>

/// THE INSERT.PHP FILE SHOULD HAVE THIS CODE
<?php
global $wpdb

$name = $_POST['name'];
$wpdb->insert( 'bank', array( 'name' => $name ), array( '%s' ) )
?>

Fatal error: Call to a member function insert() on a non-object in C:\xampp\htdocs\wordpress\wp-content\themes\poilot\insert.php on line 9

why?

when use this code; file name insert.php

insert( 'bank', array( 'name' => $name ), array( '%s' ) ) ?>