code: function(node, level, leaf) {
          var size = this.getSize(node, true), baseHeight = 0, that = this;
          if(leaf(level, node)) return size;
          if(level === 0) return 0;
          node.eachSubnode(function(elem) {
              baseHeight += that.getTreeBaseSize(elem, level -1, leaf);
          });
          return (size > baseHeight? size : baseHeight) + this.config.subtreeOffset;
      }
docs: /*
  Calculates a subtree base size. This is an utility function used by _getBaseSize_