how to add cookie.js to remember menu state

Hi,

I want to add cookie.js to a menu that will remember the state menu
jQuery cookie https://github.com/carhartl/jquery-cookie
There are some good example on the web but I cannot to adapt it to this menu and I have to use this menu
I cannot change for another one

This is the original menu js code

(function($) {
    "use strict";

    $.fn.tree = function() {

        return this.each(function() {
            var btn = $(this).children("a").first();
            var menu = $(this).children(".treeview-menu").first();
            var isActive = $(this).hasClass('active');

            //initialize already active menus
            if (isActive) {
                menu.show();
                btn.children(".fa-angle-left").first().removeClass("fa-angle-left").addClass("fa-angle-down");
            }
            //Slide open or close the menu on link click
            btn.click(function(e) {
                e.preventDefault();
                if (isActive) {
                    //Slide up to close menu
                    menu.slideUp();
                    isActive = false;
                    btn.children(".fa-angle-down").first().removeClass("fa-angle-down").addClass("fa-angle-left");
                    btn.parent("li").removeClass("active");
                } else {
                    //Slide down to open menu
                    menu.slideDown();
                    isActive = true;
                    btn.children(".fa-angle-left").first().removeClass("fa-angle-left").addClass("fa-angle-down");
                    btn.parent("li").addClass("active");
                }
            });

            /* Add margins to submenu elements to give it a tree look */
            menu.find("li > a").each(function() {
                var pad = parseInt($(this).css("margin-left")) + 10;

                $(this).css({"margin-left": pad + "px"});
            });

        });

    };

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This is what have tried  and this is not working

(function($) {
    "use strict";

    $.fn.tree = function() {

     [b]   return this.each(function(e) {
		     var checkCookie = $.cookie("nav-item");
             if (checkCookie != "") {
	         $('.treeview:eq('+checkCookie+')').addClass('active').next().show();
             }[/b]
			 
            var btn = $(this).children("a").first();
            var menu = $(this).children(".treeview-menu").first();
            var isActive = $(this).hasClass('active');

            //initialize already active menus
            if (isActive) {
                menu.show();
                btn.children(".fa-angle-left").first().removeClass("fa-angle-left").addClass("fa-angle-down");
		[b]		$.cookie("nav-item", menu);[/b]
            }
            //Slide open or close the menu on link click
            btn.click(function(e) {
                e.preventDefault();
				
                if (isActive) {
                    //Slide up to close menu
                    menu.slideUp();
                    isActive = false;
                    btn.children(".fa-angle-down").first().removeClass("fa-angle-down").addClass("fa-angle-left");
                    btn.parent("li").removeClass("active");
                } else {
                    //Slide down to open menu
                    menu.slideDown();
                    isActive = true;
                    btn.children(".fa-angle-left").first().removeClass("fa-angle-left").addClass("fa-angle-down");
                    btn.parent("li").addClass("active");
                }
            });

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Let me know if you need more code part

Thanks