It you've nested a portion of your timeline and for some reason need it not nested to make some adjustments there's a simple way to un-nest a nested sequence.
1) Find the Nest in the Browser.
2) Drag it to where you want it in the Timeline (you may need to be mindful of target tracks depending on the nest and timeline settings) but before you let go of the mouse...
3) Hold down COMMAND. That is to say, hold down COMMAND after you've begun dragging the nest into the Timeline. When you hold COMMAND you'll see the "shadow" of the nest explode to un-nested.
4) Let go of the mouse and you're done.