How to have submenu in admin panel

Hello

I am a bit new with WordPress but I am very new in developpement.
I followed a tutorial in order to add a panel in the Dashboard.
(I installed a new instence of Word press)

I added a menu name “My Panel” because of the following code.
I created a file name “wp-content/themes/twentyseventeen/my_panel.php” and I pasted the following code

<?php
add_action('admin_menu', 'my_pannel');

function my_pannel(){
	//add_menu_page('My Profile','My profile', 'author', 'my-profile','render_profile', NULL, 81);
	add_menu_page('My pannel','My pannel', 'activate_plugins', 'my-pannel','render_pannel', NULL, 6);
}

function render_pannel(){
	if(!empty($_POST)){
		var_dump($_POST);
	}
	?>
	<div class="wrap theme-options-page">
		<div id="icon-options-general" class="icon32"><br></div>
		<h2>Welcome to your profile</h2>
		<quote>To update your profile, go to Profile</quote>

		<form action="" method="post">
			<div class="theme-options-group">

				<table cellspacing="0" class="widefat options-table">
					<thead>
						<tr>
							<th colspan="2">
								Education
							</th>
						</tr>
					</thead>
					<tbody>
						<tr>
							<th>
								From
							</th>
							<td>
								<input type="text" name="from">
							</td>
						</tr>
						<tr>
							<th>
								Util
							</th>
							<td>
								<input type="text" name="until">
							</td>
						</tr>
						<tr>
							<th>
								Institut
							</th>
							<td>
								<input type="text" name="institut">
							</td>
						</tr>
					</tbody>
				</table>
			</div>
			<p class="submit">
				<input type="submit" name="send_education" class="button-primary autowidth" value="save">
			</p>
		</form>

	</div>
	<?php
}

That work fine, because now I have a men My Panel below Posts.

My question is hjwo to create now a submenu ‘education’. For exemple

My Panel
— education
— researches
— projects

That means that the above code will move to education section and not My Panel section as it is now.

many thank