private void treeList1_MouseDown(object sender, MouseEventArgs e) {
    // Check if a node's indicator cell is clicked.
    TreeListHitInfo hitInfo = treeList1.CalcHitInfo(e.Location);
    TreeListNode node = null;
    if (hitInfo.HitInfoType == HitInfoType.RowIndicator) {
        node = hitInfo.Node;
    }
    if (node == null) return;
    // Create a menu with a 'Delete Node' item.
    TreeListMenu menu = new TreeListMenu(sender as TreeList);
    DXMenuItem menuItem = new DXMenuItem("Delete Node", new EventHandler(deleteNodeMenuItemClick));
    menuItem.Tag = node;
    menu.Items.Add(menuItem);
    // Show the menu.
    menu.Show(e.Location);
}

// Deletes the node for which the command has been invoked.
private void deleteNodeMenuItemClick(object sender, EventArgs e) {
    DXMenuItem item = sender as DXMenuItem;
    if (item == null) return;
    TreeListNode node = item.Tag as TreeListNode;
    if (node == null) return;
    node.TreeList.DeleteNode(node);
}

Private Sub TreeList1_MouseDown(ByVal sender As Object, ByVal e As MouseEventArgs) _
Handles TreeList1.MouseDown
    ' Check if a node's indicator cell is clicked.
    Dim hitInfo As TreeListHitInfo = treeList1.CalcHitInfo(e.Location)
    Dim node As TreeListNode = Nothing
    If hitInfo.HitInfoType = HitInfoType.RowIndicator Then
        node = hitInfo.Node
    End If
    If node Is Nothing Then
    Return
    End If
    ' Create a menu with a 'Delete Node' item.
    Dim menu As TreeListMenu = New TreeListMenu(TryCast(sender, TreeList))
    Dim menuItem As DXMenuItem = New DXMenuItem("Delete Node", _
        New EventHandler(AddressOf deleteNodeMenuItemClick))
    menuItem.Tag = node
    menu.Items.Add(menuItem)
    ' Show the menu.
    menu.Show(e.Location)
End Sub

' Deletes the node for which the command has been invoked.
Private Sub deleteNodeMenuItemClick(ByVal sender As Object, ByVal e As EventArgs)
    Dim item As DXMenuItem = TryCast(sender, DXMenuItem)
    If item Is Nothing Then
    Return
    End If
    Dim node As TreeListNode = TryCast(item.Tag, TreeListNode)
    If node Is Nothing Then
    Return
    End If
    node.TreeList.DeleteNode(node)
End Sub