A splitter for low-voltage wire
Direct burial connectors.

Several varieties exist, silicone packed and grease packed are the most common.

You cut and strip and twist the connection(s) and insert into the cap, which then isolates, insulates and waterproofs the connection.  

They are a HUGE step up from the "vampire tap" connections that come with low priced landscape sets.  In any type of wet climate, the taps are only good for several years



Another approach is a "staked" junction box. which houses the connections for a hub distribution method.  The junction box sits atop a ground stake, keeping the wiring above ground.