insertBefore(node, child, before) {
        if (!node.children) node.children = [];
        const index = node.children.indexOf(before);
        node.children.splice(index, 0, child);
    }
Insert the child before the specified node.
@param {{}} node - The parent node.
@param {{}} child - The child node.
@param {{}} before - The node to insert before.
@returns {undefined}