A treecol is a top column of tree, Its parent must be Treecols.

<window title="tree demo" border="normal" width="400px">
    <tree id="tree" width="90%" rows="2">    
        <treecols sizable="true">        
            <treecol label="Name"/>            
            <treecol label="Description"/>            
            <treecol label="Remark"/>            
        </treecols>        
        <treechildren>        
            <treeitem>            
                <treerow>                
                    <treecell label="Item 1"/>                    
                    <treecell label="Item 1 description"/>                    
                    <treecell label="Item 1 remark"/>                    
                </treerow>                
            <treechildren>            
                <treeitem>                
                    <treerow>                    
                        <treecell label="Item 1.2"/>                        
                        <treecell label="Item 1.2 description"/>                        
                    </treerow>                    
                </treeitem>                
            </treechildren>            
            </treeitem>            
        </treechildren>        
    </tree>    
</window>