Return node ids for connecting id
to kids.
Examples
tree <- randTree(10)
# get all nodes from root to tip
getNdPtids(tree, id = "n1")
#> [1] "n2" "n3" "n4" "n5" "n6" "n7" "n8" "n9" "t1" "t2" "t3" "t4"
#> [13] "t5" "t6" "t7" "t8" "t9" "t10"