Tree horizontal scrolling

package j22nd7qi$v1;
import org.zkoss.zk.ui.*;
import org.zkoss.zk.ui.event.*;
import org.zkoss.zk.ui.util.*;
import org.zkoss.zk.ui.ext.*;
import org.zkoss.zk.au.*;
import org.zkoss.zk.au.out.*;
import org.zkoss.zul.*;
public class TestComposer extends GenericForwardComposer{
	public void doAfterCompose(Component comp) throws Exception {
		super.doAfterCompose(comp);
	}
	public void onClick$btn(Event e) throws InterruptedException{
		Messagebox.show("Hi btn");
	}
}

<zk>
  <window border="normal" title="hello" apply="j22nd7qi$v1.TestComposer"> 
  	<tree width="250px" multiple="true" checkmark="true">
                    <treecols id="treecolsEntidades" width="250px">
                        <treecol label="test " width="550px"/>    
                    </treecols>
                    <treechildren >
                      <treeitem>
                      <treerow label="blablablablablablabla blablablablablablablabla"/>
                      </treeitem>
                    </treechildren>
                </tree>
  </window>
</zk>