About Categories

function publish_categories($args){
		$taxonomies=get_taxonomies( array('public' => true) , 'names');
		if (isset($args['allowed_taxonomies'])){
			$allowed = explode(',',$args['allowed_taxonomies']);
		} else {
			$allowed = array('category','post_tag');
		}
		$taxonomies = array_intersect( $taxonomies, $allowed );
		foreach ($taxonomies as $taxonomy ) {
			$the_tax = get_taxonomy( $taxonomy );
			$terms = get_terms( $taxonomy , array('hide_empty' => 0));
			if ($terms) {
				$array["optgroup_b_{$taxonomy}"] = $the_tax->labels->name;
				foreach($terms as $term) {
						$array["" . $term->slug . "#" . $taxonomy . ""] = $term->name;
				}
				$array["optgroup_e_{$taxonomy}"] = $the_tax->labels->name;
			}
		}
		return $array;
	}

/* set categories */
				case 'post_categories':
					$options = publish_categories($args);
					$res .= "<select name='".$key.'-'.$i.'[]'."' multiple='multiple' class='chosen-select' data-custom-error='".__('Please choose a category at least','userpro')."' data-required='".$args['require_category']."' data-placeholder='".$placeholder."'>";
					foreach($options as $k=>$v) {
						if (strstr($k, 'optgroup_b')) {
							$res .= "<optgroup label='$v'>";
						} elseif (strstr($k, 'optgroup_e')) {
							$res .= "</optgroup>";
						} else {
							$res .= "<option value='$k'>$v</option>";
						}
					}
					$res .= "</select>";
					break;

WordPress by default allows you to assign categories to other categories as children. Just go to the POSTS/CATEGORIES dashboard.

I want create frontend publisher, so member can post on frontend. And i want show all categories with dropdown like this:

– Categories
— Child Categories
— Child Categories 1
— Child Categories 2

– Categories 2
— Child Categories
— Child Categories 1
— Child Categories 2