[bugfix] allow repeated values across levels when building sunburst hierarchy

[williaster]

in some cases when there are repeated values across sunburst levels, nodes for a given sequence were not always added to the correct level
e.g.,
a --> b --> b --> a
b --> a

to prevent this, this PR enforces matching level within a sequence, in addition to matching node names, when building out the sunburst hierarchy.

before

after

[landscape-bot]

Code quality remained the same when pulling 298b989 on airbnb:chris/fix-sunburst-level-trunc into 77e4d4b on airbnb:master.

[coveralls]

Coverage remained the same at 80.986% when pulling 298b989 on chris/fix-sunburst-level-trunc into 77e4d4b on master.

[mistercrunch]

👍

[landscape-bot]

Code quality remained the same when pulling a422d1b on airbnb:chris/fix-sunburst-level-trunc into 77e4d4b on airbnb:master.

[coveralls]

Coverage remained the same at 80.986% when pulling a422d1b on chris/fix-sunburst-level-trunc into 77e4d4b on master.