isInTree method
Returns true
if key
is in the tree.
Implementation
bool isInTree(K? key) {
if (key == null) return false;
if (identical(root, key)) return true;
var cursor = key;
while (true) {
var parent = getParentOf(cursor);
if (parent == null) return false;
if (identical(parent, root)) return true;
cursor = parent;
}
}