Description
As part of tskit-dev/tutorials#182 we should think of alternative ways of showing big trees. One possibility is to collapse clades in a tree if e.g. all the nodes underneath belong to the same population (or have no population). I think this is more of a viz issue than a tree-sequence manipulation issue, as it would be done per tree, and we would want to visually distinguish the collapsed clades somehow (perhaps we could use a larger triangle: I don't know if we would want to vary the triangle size depending on the number of samples in the clade).
We could allow this to happen even if e.g. a small proportion of the samples are in a different population. But then that gets pretty complicated. A more sophisticated thing would be to replace the circular internal nodes with a pie chart of the proportions of sample tips underneath the node. I guess in the viz you could specify which nodes you wanted to do this for.