Missing sub tab in build menu

[horsepwr350]

On one of my very first chars I played for a short time then made a 2nd char.  Well to make a long story short I came back to 1st char after some time. This time I had a bunch of mods  loaded with nexus mod manager  and noticed that a sub tab in my build menu ( living tree's ) was gone on 1st char. I thought it might have been a glitch but went back to the 2nd char and that sub tab was still there. I am not sure when I acquired this sub tab or not sure if its the fact that the first char was made with no mods then I returned to play it with mods enabled. when do I get the "Living tree " sub tab under decorations build menu or is it a glitch ??  if someone could answer this question that would be great. thnx