Abstract: Embodiments of the present invention relate to a method and apparatus for a runtime merging system of hierarchical trees with a reference node implementation. According to one or more embodiments of the present invention, a reference node is implemented which holds a reference to a node in a DOM tree active in memory. The reference node class allows adding nodes to the merged tree without having to make a clone of the node, which is an expensive operation. In one embodiment, if a particular node is not present below a certain level of the tree in any layer except a unique layer, it renders visiting the children of that node unnecessary. A reference is kept to the node in the memory.