<zk>
    <label multiline="true">
    1. Open tree node 1, 3, 7, 15, 31, 63, 127, 255
    2. Navigate to page 2 then navigate back to page 1
    3. Close tree node 255
    4. Should see tree node 4, 8 (bug if not seeing).
    </label>
    <window apply="org.zkoss.bind.BindComposer" viewModel="@id('vm') @init('demo.TreeVM')">
        <paging id="paging" pageSize="15" totalSize="@load(vm.totalsize)" />
        <tree id="tree" model="@load(vm.model)" mold="paging" pageSize="15" rows="15">
            <treecols>
                <treecol label="Col" />
            </treecols>
            <template name="model" var="each">
                <treeitem value="@load(each)">
                    <treerow>
                        <treecell label="${each}" />
                    </treerow>
                </treeitem>
            </template>
        </tree>
    </window>
</zk>

public class TreeVM {
    private BinaryTreeModel<String> model;
    @Init
    public void init() {
        List<String> list = new ArrayList<String>();
        for (int i = 0; i < 1000; i++) {
            list.add("" + i);
        }
        model = new BinaryTreeModel<String>(list);
    }
    public BinaryTreeModel<String> getModel() {
        return model;
    }

    public void setModel(BinaryTreeModel<String> model) {
        this.model = model;
    }
}

public class BinaryTreeModel<T> extends AbstractTreeModel<T> {

    private static final long serialVersionUID = 5067310002210333471L;
    private List<T> _tree = null;

    public BinaryTreeModel(List<T> tree) {
        super(tree.get(0));
        _tree = tree;
    }

    public boolean isLeaf(Object node) {
        return (getChildCount(node) == 0);
    }

    public T getChild(Object parent, int index) {
        int i = _tree.indexOf(parent) * 2 + 1 + index;
        if (i >= _tree.size())
            return null;
        else
            return _tree.get(i);
    }

    public int getChildCount(Object parent) {
        int count = 0;
        if (getChild(parent, 0) != null)
            count++;
        if (getChild(parent, 1) != null)
            count++;
        return count;
    }

    public int getIndexOfChild(Object arg0, Object arg1) {
        return 0;
    }
}