How to search by hierarchical taxonomy in views?
You can use Chosen Module and it supports for hiererchical select


  By default the module will automatically apply itself to any select
  elements that have more than 20 options, which is a reasonable default
  for which having Chosen will be useful. To change or disable this
  automatic enhancement, you can change the selectors (or remove all
  selectors) from the Apply Chosen to the following elements field on
  the Chosen administration page.