为什么悬停时我的下拉菜单不显示?

var app = angular.module('myApp', []);

app.controller('mainCtrl', function($scope) {
  $scope.menu = [
    ["first", 
      ["item1", "item 2"]],
    ["second", 
      ["item 1", "item 2"]]
  ];
});

li {
  list-style: none;
}

li ul {
  display: none;
}

.firstLevel {
  display: inline-block;
}

li:hover>ul {
  display: block;
  position: absolute;
}

<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script>
<div ng-app="myApp" ng-controller="mainCtrl">
  <ul>
    <div ng-repeat="m in menu" class="firstLevel">
      <li>
        <a href="#">{{m[0]}}-</a>
      </li>
      <li>
        <ul>
          <div ng-repeat="msub in m[1]">
            <a>{{msub}}</a>
          </div>
        </ul>
      </li>
    </div>
  </ul>
</div>