buildTree method
Implementation
IntervalRTreeNode buildTree() {
// sort the leaf nodes
leaves.sort(nodeComparator);
// now group nodes into blocks of two and build tree up recursively
List src = leaves;
List? temp = null;
List dest = [];
while (true) {
buildLevel(src, dest);
if (dest.length == 1) return dest[0];
temp = src;
src = dest;
dest = temp;
}
}