set.seed(1)
## Generate a random ultrametric tree
tree <- rcoal(20)
## Add some node labels
tree$node.label <- letters[1:19]
## Add its root time
tree$root.time <- max(tree.age(tree)$ages)
## Slice the tree at age 0.75
tree_75 <- slice.tree(tree, age = 0.75, "deltran")
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