$*$I need most explanation on part $($d$),$ thank you so very much$*$

A Cayley tree is a network generating model that produces a symmetric tree constructed from a

central node of degree $k.$ Each node at distance $d$ from the central node has degree $k$ until we reach the nodes at distance D that have degree $1$; these nodes are called "leaves."

$($a$)$ Determine a formula for the number of nodes reachable in T steps from the central node for a general Cayley Tree.

$($b$)$ Find an expression for the diameter $l_{\text{m}\text{a}\text{x}}$ as a function of the total number of nodes $N$ and $k.$

$($c$)$ Does the network display the small$-$world property? Consider when $kN.$

$($d$)$ Use NetworkX to generate a Cayley Tree where each node has degree $k=3$ and the leaves are at distance $D=4$ from the root. There are many ways to do this including manually growing the tree$).$ You can use the balanced$\_$tree generator and prune the tree as well. Draw the Cayley tree using the $nx.$draw$\_$kamada$\_$kawai function.

For your reference, here is a Cayley Tree with $k=3$ and $D=5.$