Assuming you want to create a category filer for smart search.You don't need a web part. What you are trying to accomplish can be done without it.
I use checkbox list as example, but you can render drop down or radio button list or whatever you want. It will be even more simple.
Create a TEXT/XML transformation under for example Root page type, call it CategoryCheckboxList:
<input type="checkbox" name="CategoryID" id="cat{%CategoryID%}" value="{%CategoryID%}"><label for="cat{%CategoryID%}">{%CategoryDisplayName%}</label><br/>
Now. Go to your page and add static text web part and put macro inside:
{% GlobalObjects.Categories.Where("CategoryParentID = 1111").ApplyTransformation("CMS.Root.CategoryCheckboxList")|(identity)GlobalAdministrator%}
This is just a general idea. Smart search filter is limited in terms of layout and design. I can share more if you are interested.