Use this if you are using igraph from R
| make_tree {igraph} | R Documentation | 
Create a k-ary tree graph, where almost all vertices other than the leaves have the same number of children.
make_tree(n, children = 2, mode = c("out", "in", "undirected"))
tree(...)
| n | Number of vertices. | 
| children | Integer scalar, the number of children of a vertex (except for leafs) | 
| mode | Defines the direction of the
edges.  | 
| ... | Passed to  | 
An igraph graph
Other deterministic constructors: 
graph_from_atlas(),
graph_from_edgelist(),
graph_from_literal(),
make_chordal_ring(),
make_empty_graph(),
make_full_citation_graph(),
make_full_graph(),
make_graph(),
make_lattice(),
make_ring(),
make_star()
make_tree(10, 2)
make_tree(10, 3, mode = "undirected")