Code below shows an example of how to scroll current SideBarPanel using MouseWheel:

private void frm_Load(object sender, EventArgs e)
        {
            sideBar1.MouseMove += new MouseEventHandler(sideBar1_MouseMove);
            sideBar1.MouseWheel += new MouseEventHandler(sideBar1_MouseWheel);
      }

        void sideBar1_MouseMove(object sender, MouseEventArgs e)
        {
            sideBar1.Focus();
        }

        void sideBar1_MouseWheel(object sender, MouseEventArgs e)
        {
            if (e.Delta < 0)
            {
                if (sideBar1.ExpandedPanel.TopItemIndex < sideBar1.ExpandedPanel.SubItems.Count - 1)
                    sideBar1.ExpandedPanel.TopItemIndex = sideBar1.ExpandedPanel.TopItemIndex + 1;
            }
            else
            {
                if (sideBar1.ExpandedPanel.TopItemIndex > 0)
                    sideBar1.ExpandedPanel.TopItemIndex = sideBar1.ExpandedPanel.TopItemIndex - 1;
            }
        }