@using Mvc.CascadeDropDown

//First simple dropdown 
@Html.DropDownListFor(m=>m.SelectedCountry, Model.Countries,
"Please select a Country", new {@class="form-control"})

//Dropdown list for SelectedCity property that depends on selection of SelectedCountry property
@Html.CascadingDropDownListFor( 
      expression: m => m.SelectedCity, 
      triggeredByProperty: m => m.SelectedCountry,  //Parent property that trigers dropdown data loading
      url: Url.Action("GetCities", "Home"),  //Url of action that returns dropdown data
      actionParam: "country",   //Parameter name for the selected parent value that url action receives
      optionLabel: "Please select a City", // Option label
      disabledWhenParrentNotSelected: true, //If true, disables dropdown until parrent dropdown selected
      htmlAttributes: new { @class = "form-control" }) //Html attributes

//Dropdown list for SelectedStreet property that depends on selection of SelectedCity property
@Html.CascadingDropDownListFor(m => m.SelectedStreet, m => m.SelectedCity, 
Url.Action("GetStreets", "Home"), "city", "Please select a Street", true, new { @class = "form-control" })