yeah, I have a feeling the only "safe" solution would be for me to spread my tikz learning document into 2 documents. The issue is when I add a ```[split circle] \nodepart{lower} 21``` to the node displaying 20 in this tree:
```
\begin{tikzpicture}[
every node/.style={circle, fill=black!20},
level distance=1cm,
level 1/.style={sibling distance=5.5cm},
level 2/.style={sibling distance=3cm},
level 3/.style={sibling distance=1.5cm}
]
\node (a) {1}
child { node{2}
child { node{4}
child { node{8} }