You can define menu in adminCP in file Install.php

protected function setOthers()
{
    $this->admincp_menu = [
        "Manage Campaigns" => "betterads",
        "Add Placement" => "betterads.addplacement",
        "Manage Placements" => "betterads.placement",
        "Manage Invoice" => "betterads.invoice",
        "Manage Sponsorships" => "betterads.sponsor",
    ];//Do not put admincp here
    $this->admincp_route = 'admincp.betterads';//must be begun with admincp
}