Some suggestions:

• Use var when declaring variables, unless you really want to make global variables (which you probably don't)

• Combine var statements using ,

   var a = 1, b = 2, c = 3;
  

• Combine classes in toggleClass

   $(this).toggleClass('minus expand')
  

• Cache selectors that are used often (like $('#main'))

• You don't need to use $li2 inside the click handler, you can just use $(this)

• Turn repeated code into a function

$(function(){
    var $main('#main'),
    slide = function(ele, find){
        return $(ele).toggleClass('minus expand').find(find).delay(200).slideToggle(400);
    },
    $li = $('> li.expand', $main).click(function(){
        var $ul = slide(this, 'ul.sub-level');
        $('> li > ul', $main).not($ul).slideUp('slow');
        $('> li.minus', $main).not(this).toggleClass('minus expand')
    }),
    $li2 = $('.sub-level > li.expand').click(function(){
       slide(this, 'ul.sub-level2');
    });
});

Some suggestions:

• Use var when declaring variables, unless you really want to make global variables (which you probably don't)

• Combine var statements using ,

   var a = 1, b = 2, c = 3;
  

• Combine classes in toggleClass

   $(this).toggleClass('minus expand')
  

• Cache selectors that are used often (like $('#main'))

• You don't need to use $li2 inside the click handler, you can just use $(this)

• Turn repeated code into a function

$(function(){
    var $main = ('#main'),
    slide = function(ele, find){
        return $(ele).toggleClass('minus expand').find(find).delay(200).slideToggle(400);
    },
    $li = $('> li.expand', $main).click(function(){
        var $ul = slide(this, 'ul.sub-level');
        $('> li > ul', $main).not($ul).slideUp('slow');
        $('> li.minus', $main).not(this).toggleClass('minus expand')
    }),
    $li2 = $('.sub-level > li.expand').click(function(){
       slide(this, 'ul.sub-level2');
    });
});

Some suggestions:

• Use var when declaring variables, unless you really want to make global variables (which you probably don't)

• Combine var statements using ,

• Combine classes in toggleClass

   $(this).toggleClass('minus expand')
  

• Cache selectors that are used often (like $('#main'))

• You don't need to use $li2 inside the click handler, you can just use $(this)

• Turn repeated code into a function

$(function(){
    var $main('#main'),
    slide = function(ele, find){
        return $(ele).toggleClass('minus expand').find(find).delay(200).slideToggle(400);
    },
    $li = $('> li.expand', $main).click(function(){
        var $ul = slide(this, 'ul.sub-level');
        $('> li > ul', $main).not($ul).slideUp('slow');
        $('> li.minus', $main).not(this).toggleClass('minus expand')
    }),
    $li2 = $('.sub-level > li.expand').click(function(){
       slide(this, 'ul.sub-level2');
    });
});

Some suggestions:

• Use var when declaring variables, unless you really want to make global variables (which you probably don't)

• Combine var statements using ,

   var a = 1, b = 2, c = 3;
  

• Combine classes in toggleClass

   $(this).toggleClass('minus expand')
  

• Cache selectors that are used often (like $('#main'))

• You don't need to use $li2 inside the click handler, you can just use $(this)

• Turn repeated code into a function

$(function(){
    var $main('#main'),
    slide = function(ele, find){
        return $(ele).toggleClass('minus expand').find(find).delay(200).slideToggle(400);
    },
    $li = $('> li.expand', $main).click(function(){
        var $ul = slide(this, 'ul.sub-level');
        $('> li > ul', $main).not($ul).slideUp('slow');
        $('> li.minus', $main).not(this).toggleClass('minus expand')
    }),
    $li2 = $('.sub-level > li.expand').click(function(){
       slide(this, 'ul.sub-level2');
    });
});