Treeitem contains a row of data (treerow), and an optional treechildren.

If the component doesn't contain a treechildren, it is a leaf node that doesn't accept any child items.

If it contains a treechildren, it is a branch node that might contain other items.

For a branch node, an +/- button will appear at the beginning of the row, such that user could open and close the item by clicking on the +/- button.

<window title="tree demo" border="normal" width="400px">
    <tree id="tree" width="90%" >    
        <treecols sizable="true">        
            <treecol label="Name"/>            
            <treecol label="Description"/>            
        </treecols>        
        <treechildren>        
            <treeitem>            
                <treerow>                
                    <treecell>                    
                        <image src="/img/folder.gif"/>Item 1                        
                    </treecell>                    
                    <treecell>                    
                        <textbox value="Item 1 description"/>                        
                    </treecell>                    
                </treerow>                
            </treeitem>            
            <treeitem>            
                <treerow>                
                    <treecell label="Item 2"/>                    
                    <treecell label="Item 2 description"/>                    
                </treerow>                
                <treechildren>                
                    <treeitem open="false">                    
                        <treerow>                        
                            <treecell label="Item 2.1">                            
                                <image src="/img/folder.gif"/>                                
                            </treecell>                            
                        </treerow>                        
                        <treechildren>                        
                            <treeitem>                            
                                <treerow>                                
                                    <treecell label="Item 2.1.1"/>                                    
                                </treerow>                                
                            </treeitem>                            
                        </treechildren>                        
                    </treeitem>                    
                </treechildren>                
            </treeitem>            
            <treeitem label="Item 3"/>            
        </treechildren>        
    </tree>    
</window>