Use this if you are using igraph from R
Create a regular tree graph.
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 determimistic 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")