how to get check box data in the cell

below program to list box within list box, check box are there
user click the checkbox
that information should come in cell,
difference between to checkbox selected add ","(comma)

Option Explicit

Private Sub UserForm_Initialize()
Me.ListBox1.List = WorksheetFunction.Transpose(Range("A1:A13"))
End Sub

Private Sub CommandButton2_Click()
Call SelectDeselect(True)
End Sub

Private Sub CommandButton3_Click()
Call SelectDeselect(False)
End Sub

Private Sub SelectDeselect(bu As Boolean)
Dim i&
With Me.ListBox1
    For i = 0 To .ListCount - 1
        .Selected(i) = bu
    Next i
End With
End Sub

Private Sub CommandButton1_Click()
Unload Me
End Sub