how tree widget works in ofbiz

[javed]

hello guy's i am new to ofbiz. i dont know most of the things about ofbiz. can any one tell me how tree widget works. because i am trying simple tree which will show primary key and name belongs to it. but it not working. i used entity-one tag in tree root node

here is my code

 <tree name="OfBizDemoTree" entity-name="OfbizDemo" root-node-name="node-root">
        <node name="node-root" render-style="simple">
            <sub-node node-name="node-body">
               <entity-and entity-name="OfbizDemo">
                    <field-map field-name="ofbizDemoTypeId" from-field=""/>
                    <order-by field-name="ofbizDemoTypeId DESC"/>
               </entity-and>
            </sub-node>
        </node>
</tree>

and what is the entity-and tag. and attributes of field-map field-name and from-field means what?