How to add arrays VueJS?

I have an array desserts that i am looping over to get the list of my desserts. Now i have another array moreDesserts that renders some checkboxes with value and i when i select a checkbox, it's value gets added to the selectedDessert array in the vuex. I am trying to create a method such that when a user selects a checkbox and clicks on the button ADD ARRAYS the selected array should be concatenated to the desserts array. I have created the mutation addArrays but that doesn't seem to be adding the arrays.

Please check this working CodeSandbox.

Here is my HelloWorld Component:

    <template>
  <div class="ml-3">
    <v-flex v-for="el in getDesserts" :key="el.name">
      <div class="title mt-2">{{el.name}}</div>
    </v-flex>
    <v-flex v-for="dessert in getMoreDesserts" :key="dessert.fat">
      <v-checkbox v-model="selectedDessert" :label="dessert.name" :value="dessert"></v-checkbox>
    </v-flex>
    <v-btn @click="addArrays">Add Arrays</v-btn>
  </div>
</template>

<script>
import { mapGetters } from "vuex";
export default {
  name: "HelloWorld",
  data() {
    return {};
  },
  computed: {
    ...mapGetters({
      getDesserts: "getDesserts",
      getMoreDesserts: "getMoreDesserts",
      getSelectedDessert: "getSelectedDessert"
    }),
    selectedDessert: {
      get() {
        return this.getSelectedDessert;
      },
      set(val) {
        return this.$store.commit("setSelectedDessert", val);
      }
    }
  },
  methods: {
    addArrays() {
      this.$store.commit("addArrays");
      console.log(this.selectedDessert);
    }
  }
};
</script>

This is my Vuex Store:-

import Vue from "vue";
import Vuex from "vuex";

Vue.use(Vuex);

export default new Vuex.Store({
  state: {
    desserts: [
      { name: "Yogurt", calories: 169, fat: 22.0 },
      { name: "Chocolate", calories: 270, fat: 19.2 }
    ],
    moreDesserts: [
      { name: "Ice Cream", calories: 280, fat: 14.0 },
      { name: "Cake", calories: 400, fat: 35.0 }
    ],
    selectedDessert: []
  },
  getters: {
    getMoreDesserts: state => state.moreDesserts,
    getSelectedDessert: state => state.selectedDessert
  },
  mutations: {
    setSelectedDessert(state, payload) {
      state.selectedDessert = payload;
    },
   addArrays(state) {
     state.desserts.concat(state.selectedDessert);
     state.selectedDessert = [];
    },
  },
  actions: {}
});

Any help will be appreciated. Thank you.