The preferred way to install this extension is through composer.
Add to the require section of your composer.json file:
"mimicreative/yii2-metismenu": "~1.0"
And run in terminal
composer update
Use as the asset bundle in Yii2 View files.
// write this in your view file or layout
\mimicreative\assets\MetisMenuAsset::register($this);
Or maybe you prefer to include it in your asset dependency.
public $depends = [
// ...
'mimicreative\assets\MetisMenuAsset',
// ...
];