Multiple check box not working when it's value same vuejs

When I check Apple it's all check Pineapple. When I unchecked Pineapple it's also unchecked Apple. both Tag id different. How can I check only one Apple instead of Pineapple?

var demo = new Vue({
  el: '#demo',
  data: {
    checkedNames: []
  },
  computed: {
    computedNames() {
      let names = this.checkedNames;
      return names.toString();
    }
  }
})

<script src="https://cdn.jsdelivr.net/npm/vue/dist/vue.min.js"></script>
<div id="demo">
  <input type="checkbox" id="50" value="50" v-model="checkedNames">
  <label for="Apple">Apple</label>
  <input type="checkbox" id="51" value="51" v-model="checkedNames">
  <label for="Banana">Banana</label>
  <input type="checkbox" id="52" value="50" v-model="checkedNames">
  <label for="Pineapple">Pineapple</label>
  <br>
  <span>Checked names: </span>
  <span>Computed names (reversed order): </span>
</div>