This what I found at the Codex about
add_menu_page( $page_title, $menu_title, $capability, $menu_slug, $function, $icon_url, $position );
$position
(integer) (optional) The position in the menu order this menu should appear. By default, if this parameter is omitted, the menu will appear at the bottom of the menu structure. The higher the number, the lower its position in the menu. WARNING: if two menu items use the same position attribute, one of the items may be overwritten so that only one item displays! Risk of conflict can be reduced by using decimal instead of integer values, e.g. 63.3 instead of 63 (Note: Use quotes in code, IE ‘63.3’).
