Yes, BGMPLAY has the track number as an argument. You can play up to 7 song at the same time. You can even use some tracks to do "sound effects" using MML.
You need to define your song with BGMSET before using BGMPLAY.
Example
BGMSET 128,"CDEF"
BGMSET 129,"BBBBBB"
BGMPLAY 0,128
BGMPLAY 1,129
1そうだね プレイ済み