using DevExpress.Web.ASPxTreeList;

protected void Page_Load(object sender, EventArgs e) {
    ASPxTreeList1.SettingsEditing.AllowRecursiveDelete = true;
}
protected void ASPxTreeList1_CustomCallback(object sender,
TreeListCustomCallbackEventArgs e) {
    foreach (TreeListNode node in ASPxTreeList1.GetSelectedNodes())
        ASPxTreeList1.DeleteNode(node.Key);
    ASPxTreeList1.DataBind();
}

Imports DevExpress.Web.ASPxTreeList

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs)
    ASPxTreeList1.SettingsEditing.AllowRecursiveDelete = True
End Sub

Protected Sub ASPxTreeList1_CustomCallback(ByVal sender As Object, _
ByVal e As TreeListCustomCallbackEventArgs)
    For Each node As TreeListNode In ASPxTreeList1.GetSelectedNodes()
        ASPxTreeList1.DeleteNode(node.Key)
    Next node
    ASPxTreeList1.DataBind()
End Sub

<dxe:ASPxButton ID="ASPxButton1" runat="server" AutoPostBack="False"
    CssFilePath="~/App_Themes/Glass/{0}/styles.css"
    CssPostfix="Glass" OnClick="ASPxButton1_Click" Text="Delete Selected"
    EnableClientSideAPI="True">
    <ClientSideEvents Click="function(s, e) {
        treeList.PerformCallback('');
    }" />
</dxe:ASPxButton>