I do lots of mindmaps recently and I often face a problem which is that I can't merge branches. Such as a node has branch1, branch2, branch3 and branch4, and I find branch3 and branch4 can tend to another node. But, it seems both MindNode and Xmind don't support this function and are all one straight way.
Can any software provide the function in the red box? Thanks a lot!
You should probably be looking for a concept mapping software rather than a mindmapping one. Unlike mind maps, concept maps are general graphs rather than trees.
Also Wikipedia has an article that lists some concept- and mind-mapping software.