# a chain with branches. Despite the branches defined first,
# the output should create one chain with branches going up/down

 [ Bonn ] --> [ Berlin ]
 [ Berlin ] --> [ Koeln ]
 [ Berlin ] --> [ Cottbus ]
 [ Koeln ] --> [ Frankfurt ]
 [ Frankfurt ] --> [ Chemnitz ]
 [ Frankfurt ] --> [ Dresden ]
 [ Frankfurt ] --> [ Hannover ]
 [ Hannover ] --> [ Hamburg ]