The default action is Overlay. You need to learn to use the Modifier keys in Premiere Pro. You will notice that there are fewer tools – but the tools are really still there. They are just combined with other tools and require the use of a Modifier key. In this case, the Ctrl key changes overlay to insert.
Single Track is selected by using the “M” key. Once selected, use the Shift key to change from single track to Multi-Track.
If you select a tool, like the Select tool (V), and hover over a clip in the sequence, you will see instructions in the status bar to use modifiers. As you press each modifier, the instructions change.
Steven
Adobe Premiere Pro 1.5.1 / After Effects 6.5 Pro https://www.stevengotz.com
Learning Adobe Premiere Pro 1.5 https://www.lynda.com
Contributing Writer, PeachPit Press, Visual QuickPro Guide, Premiere Pro 1.5