By the way, regarding branching off (not just) high-speed lines, that is a constant hobby-horse of mine...

The simplest solution is branching like a tree:

No superstructures, just four switches (like the one below: not only the end but the centerpiece is movable, too), one train passes three of them.

But such a simple bifurcation (AFAIK the one at Courtalain on the LGV Atlantique was such for some transitional time) is a bottleneck. To allow two trains to pass, you need at least one bridge:

If train control foresees switching tracks there must be such switches on one arm. So one superstructure, six switches, one train passes 3(4). Most high-speed line connections and bifurcations are like this.   Most of them in Italy, as the Italian high-speed philosophy involves connections to conventional lines every 30-50 km, often built out in a pharaonic way:

On a very busy line, it would be ideal if track-changing at the branching would be level-separated, too. What to do? One could double the tree:

But 4 superstructures, 14 switches, every train passing 5 -- expensive, and this number of routes is overkill. The following still  does all 12 cases, but spares 2-2 bridges and switches, and switch passages for one train can be 3-4.

_{*Lunatic*, n.
One whose delusions are out of fashion.}