Timeline as Source

Let's say I have an existing Timeline with content on it called "A".

I'm trying to create another Timeline called "B" using parts of Timeline "A".

So I'm using Speed Editor to cut parts of "A" from the Source Bin.

When I select the "Source" key on the speed editor my existing timeline "A" is disappearing.

Any way I can use the Timeline as my source?

On the Edit page it's simple.

Just load A into the Source Viewer and edit as normal.