The B major thirteenth chord is a 6-note chord consisting of the notes B, D#, F#, A#, C# and G#.
You can see these notes highlighted in the interactive piano chart below.
The chord itself is often abbreviated as Bmaj13.
Interactive piano diagram for the B major thirteenth chord
Chords that are a subset of Bmaj13. These contain less notes but all of them are included in Bmaj13.