macro to copy excel files only from main directory and sub directory to a specific folder

I have a folder on c:\\backup2018.

In this folder there are folders as e,g folder1, folder 2 and so on but however there may be subfolders folder1 or any any folders on c:\\backup2018..

In all folders there are pdf ,zip files, excel files xls, xlsm, xlsx, xlsb, text files, word files.

Looking a macro to copy all excel files xls, xlsm, xlsx, xlsb, of c:\\backup2018\folder 1 , folder2 with their subfolders to C:\Users\user\documents \excelfilesbackup2018

I have found a code while googling but works only in source folder only . It does not look in sub folders.

c:\\test\\folder\folder1

c:\\test\\folder\
c:\\test\\folder\folder2/folder3

Can any one assist to modify for code to search for all excel extensions xl*

Sub CopyExcelFilesOnly()
Dim MyFSO As FileSystemObject
Dim MyFile As File
Dim SourceFolder As String
Dim DestinationFolder As String
Dim MyFolder As Folder
Dim MySubFolder As Folder

SourceFolder = "C:\test"
DestinationFolder = "C:\all"

Set MyFSO = New Scripting.FileSystemObject
Set MyFolder = MyFSO.GetFolder(SourceFolder)

For Each MyFile In MyFolder.Files
    If MyFSO.GetExtensionName(MyFile) = "xlsx" Then
        MyFSO.CopyFile Source:=MyFSO.GetFile(MyFile), _
        Destination:=DestinationFolder & "\" & MyFile.Name, Overwritefiles:=False
    End If
Next MyFile

End Sub