Question about how a branch is made


I am a bit puzzled about how the
As shown in the pictures below,
The two cases has the same divergence branch length
May I know what makes two cases separated in different branches when the branch length is in “time”?

Are they already separated into different branches even in divergence mode?
But they have the same number of nucleotide mutation (Actually they are both B.1.36.27), I suppose they should be grouped and shown in the same cluster.