Nodes are not reused properly when adding/removing them

[kachkaev]

Hey guys!

Looks like there is an issue with how d3 reuses nodes. Here is what's happening when I add three leafs to a list at the very top one by one and then remove them (also one by one):

The second (the largest) state branch is not affected at all, but there's quite a lot going on visually.

Those strange unexpected horisontal jumps probably happen because of how d3 treats ids of the nodes. If they are represented as an array and id = i, adding or removing an item in the middle of it is likely to bring in this effect.