I've looked at knot literature but haven't found a name for this, so I named it. The basic knot is well known; it's called a "lark's head". Since all I've done is to slip the two ends through the lark's head to make a noose, I call it that.
WARNING: Don't use this knot when human safety would depend on it. Climbers and mountaineers have well-tested, reliable knots for such situations.
Step 1: Double the Cord Over
Step 2: Form the Lark's Head
You've made a lark's head. Move the crossing cord a little farther from your hand, so there's a clear opening through the two half-loops.
Step 3: Form the Noose
Step 4: Tightening, Retightening, and Locking
A springy bundle probably still feels loose. If so, compress the bundle and get a new grip on the cords. Rest your foot on the bundle, on the cords nearest the lark's head, and pull to slide the lark's head tighter.
To make the knot more permanent, you can lock it. Make an overhand in the cord ends. (Exactly like the first step in tying shoelaces.) With your foot still on the bundle, pull on the cords and move your hands apart until you're pulling in opposite directions. You have just locked the lark's head, and you can trust it to stay that way.(*)
But, let's say that later on you want to loosen the locked knot. Again put your foot on the bundle and cords nearest the lark's head, hold the two cord ends together, and pull. This makes a little slack between the overhand and the lark's head so you can untie the overhand.
In twine or small string, the locking overhand knot may be difficult to undo. Use a shoelace knot instead of an overhand, and it'll unlock easily.
(*) If you're using slippery cord, like polypropylene, an overhand may not lock securely. You may want to tie another overhand knot. For added security, wrap a short length of duct tape around the two cords, close to the knot.