Bootstrap Select - reinitialize on dynamically added element

You have to refresh your select as mentioned on the plugin page

$(select).selectpicker('refresh');

refresh()

To programmatically update a select with JavaScript, first manipulate the select, then use the refresh method to update the UI to match the new state. This is necessary when removing or adding options, or when disabling/enabling a select via JavaScript.

$(".selectpicker").selectpicker('refresh');

Demo