How to always keep ng-multiselect-dropdown open?

Question

https://www.npmjs.com/package/ng-multiselect-dropdown

I am using this ng multiselect dropdown in angular and I want to keep it always open. I tried using defaultOpen option but it goes away soon.

HTML CODE:

    <ng-multiselect-dropdown
  [placeholder]="'custom placeholder'"
  [settings]="dropdownSettings"
  [data]="dropdownList"
  [(ngModel)]="selectedItems"
  (onSelect)="onItemSelect($event)"
  (onSelectAll)="onSelectAll($event)"
>
</ng-multiselect-dropdown>

TS CODE:

import { Component, OnInit } from '@angular/core';
import { IDropdownSettings } from 'ng-multiselect-dropdown';

export class AppComponent implements OnInit {
  dropdownList = [];
  selectedItems = [];
  dropdownSettings = {};
  ngOnInit() {
    this.dropdownList = [
      { item_id: 1, item_text: 'Mumbai' },
      { item_id: 2, item_text: 'Bangaluru' },
      { item_id: 3, item_text: 'Pune' },
      { item_id: 4, item_text: 'Navsari' },
      { item_id: 5, item_text: 'New Delhi' }
    ];
    this.selectedItems = [
      { item_id: 3, item_text: 'Pune' },
      { item_id: 4, item_text: 'Navsari' }
    ];
    this.dropdownSettings:IDropdownSettings = {
      singleSelection: false,
      idField: 'item_id',
      textField: 'item_text',
      selectAllText: 'Select All',
      unSelectAllText: 'UnSelect All',
      itemsShowLimit: 3,
      allowSearchFilter: true
    };
  }
  onItemSelect(item: any) {
    console.log(item);
  }
  onSelectAll(items: any) {
    console.log(items);
  }
}