Help - Collapsing nodes
To collapse a node means to delete this node and add its child nodes to its parent node. Therefore you cannot perform this operation on the root node. You could e.g. use this option if you feel that the respective node is not well supported and you want to show a polytomy instead.
To perform a collapse operation select the node you want to collapse and choose Collapse node from the edit menu or the context menu or use the keyboard shortcut Ctrl + Del.
Branch length
If the collapsed branch has a defined length, this length will be added to all child branches which also have a defined length during the operation. If you use this operation in e.g. a chronogram, this means all nodes in the subtree under the collapsed node will still have the same horizontal position. Branches which do not have a specified branch length, still won't have one after this operation.
Note that branch lengths have not been treated this way before version 2.0.55. Before that the collapsed node was simply deleted and the branch lengths of child nodes remained unchanged.
Example
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