Out-tree:
directed: true
vcount: 5
edges: {
4 0
3 4
4 1
1 2
}

In-tree:
directed: true
vcount: 5
edges: {
0 4
4 3
1 4
2 1
}

Undirected tree:
directed: false
vcount: 5
edges: {
4 0
4 3
4 1
2 1
}

Forest:
directed: true
vcount: 5
edges: {
4 1
3 4
1 2
}

Edgeless graph:
directed: true
vcount: 5
edges: {
}

Null graph:
directed: true
vcount: 0
edges: {
}
