Stacking branches on joining lists

Hi everyone,

I'm having a bit of trouble figuring this out.

this are actually a number of 6x6 matrixes, so these trees will be always something like {n,6}(6)

the thing is, the way i need the definition to work, i want to join a number of trees like these thogeter. for example: 
suppose i have one tree with {0,6}(6) and {1,6}(6) and another tree with {0,6}(6)
and i need to get them to be 0, 1 and {2,6}(6)

How hard is this? maybe there is a component to do it that i don't know of?

thanks!