Laravel error:: Illegal string offset 'category_name'

I'm trying to create an admin side form. Here i'm trying to select data from the database. Also i want to display it. But for some reason it's not working. Here's my controller code,

public function save()
{
  if (Input::has('save'))
  {
    $rules = array('category_name' => 'required|min:1|max:50', 'parent_category' => 'required');
    $input = Input::all();
    $messages = array('category_name.required' =>'Please enter the category name.', 'category_name.min' => 'Category name must be more than 4 characters', 'category_name.max' =>'Category name must not be more than 15 characters!!!',  'parent_category.required' => 'Please Select  Parent Category.',);
    $validator = Validator::make($input, $rules, $messages);

    if ($validator->fails()) 
    {
        return Redirect::to('admin/category/add')->withErrors($validator)->withInput($input); 
    }
    else
    {       
        $insert_db = CategoryModel::insert($input);
        $selected_category = CategoryModel::select($input['category_name']);
    }
  } 
}

and my CategoryModel.php is following.

public static function insert($values)
{
      $insert  = DB::table('add_category')->insert(array('category_name'=>$values['category_name'], 'parent_category'=>$values['parent_category']));
      if(isset($insert))
      { 
        echo 'inserted successfully';
      }  
      else 
      {
        echo 'Failed';
       }        
}

public static function select($values)
{
      $insert = DB::table('add_category')->where('category_name' . '=' . $values['category_name']);
}