public class BootstrapFileManagerSettingsToolbar :
    FileManagerSettingsToolbar

Public Class BootstrapFileManagerSettingsToolbar
    Inherits FileManagerSettingsToolbar

<dx:BootstrapFileManager runat="server" ID="FileManager1">
    <SettingsToolbar>
        <Items>
            <dx:BootstrapFileManagerToolbarCustomDropDownButton >
                <Items>
                    <dx:BootstrapFileManagerToolbarCustomButton Text="Default User" CommandName="DefaultUser" />
                    <dx:BootstrapFileManagerToolbarCustomButton Text="Document Manager" CommandName="DocumentManager" />
                    ...
                </Items>
            </dx:BootstrapFileManagerToolbarCustomDropDownButton>
        </Items>
    </SettingsToolbar>
</dx:BootstrapFileManager>