widget.xml

<?xml version="1.0" encoding="UTF-8"?>
<widgets xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Widget:etc/widget.xsd">
	<widget id="nicolasbejean_categorywidget" class="NicolasBejean\CategoryWidget\Block\Widget\CategoryWidget">
		<label>widget_label</label>
		<description>widget_description</description>
		<parameters>
            <parameter name="widget_title" xsi:type="text" visible="true" sort_order="1">
                <label>widget_title</label>
            </parameter>
            <parameter name="widget_content" xsi:type="text" visible="true" sort_order="2">
                <label>widget_content</label>
            </parameter>
			<parameter name="category_selection" xsi:type="multiselect" visible="true" sort_order="3" source_model="NicolasBejean\CategoryWidget\Model\Config\Source\CategoryList">
                <label>category_selection</label>
                <description>category_selection_description</description>
            </parameter>
            <parameter name="category_image_width" xsi:type="text" visible="true" sort_order="4">
                <label>category_image_width</label>
                <description>category_image_width_description</description>
            </parameter>
            <parameter name="category_image_height" xsi:type="text" visible="true" sort_order="5">
                <label>category_image_height</label>
                <description>category_image_height_description</description>
            </parameter>
            <parameter name="template" xsi:type="select" required="true" visible="true" sort_order="6">
                <label>template</label>
                <options>
                    <option name="img_background" value="widget/category_widget_img_background.phtml" selected="true">
                        <label>default_template</label>
                    </option>
                    <option name="default" value="widget/category_widget.phtml">
                        <label>other_template</label>
                    </option>
                </options>
            </parameter>
		</parameters>
	</widget>
</widgets>