It looks like you're trying to build a tree; if that's the case, this mapping should work fine, otherwise you could just replace the "Children" inverse bag with a "Child" property. You may need to modify the id and generator elements to suit your needs as well.
Code:
<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="YourApp" namespace="YourApp.Namespace">
<class name="Table1" table="Table1">
<id name="Id" column="id" type="Int64">
<generator class="identity"/>
</id>
<property name="Name" column="name"/>
<many-to-one class="Table1" name="Parent" column="parentId" cascade="save-update"/>
<bag name="Children" cascade="save-update" inverse="true">
<key column="parentId"/>
<one-to-many class="Table1"/>
</bag>
</class>
</hibernate-mapping>