#NEXUS
BEGIN TAXA;
dimensions ntax=8;
taxlabels A B C D E F G H;
END;
BEGIN CHARACTERS;
dimensions nchar=6;
format datatype=protein missing=? gap=-;
charlabels one two three four five six;
matrix
A WITH-B
B WITH-A
C WITH-D
D WITH-C
E WITH-F
F WITH-E
G WITH-H
H WITH-G;
END;
BEGIN TREES;
tree bush_branchlength_negative = (((A:1,B:1):1,(C:1,D:1):-0.25):1,((E:1,F:1):1,(G:1,H:1):1):1);
END;