siblings = [*; subtree 920; subtree 950]
}, * filled by subtree 500;
siblings = [subtree 20; *; subtree 80]
}, * filled by subtree 50
siblings = [*; subtree 920; subtree 950]
}, * filled by subtree 500;
siblings = [subtree 20; *; subtree 80]
}, * filled by subtree 50