Show bus concatenation in schematic
In KiCad, you denote a bus-bus connection with a junction dot like this:



Here, the numeric suffixes denote which members are connected. PCA0 and ADR0 are connected.  PCA5, ADR5 and BUS5 are also connected.  NOTE: PCA11 - PCA15 are not connected in this diagram.

See KiCad Eeschema Documentation for more details.



Edit to include mechanism for joining non-identical bus suffixes

Suppose you want to concatenate two buses A[0..7] and B[0..7] with the larger bus C[0..15]. The following image illustrates how you might approach this:



Here, we create elements for B that did not previously exist.  Once they exist, you can join A[0..7] to B[8..15] and C[0..15] to get a bus concatenation.