I wanted to make an addition:

by changing both ".tree ul" selector to :

.tree ul {

display: flex;

flex-wrap: nowrap;

padding-top: 20px;

position: relative;

transition: all 0.5s;

-webkit-transition: all 0.5s;

-moz-transition: all 0.5s;

}

you can now auto-scale the width of this chart component, in case you have a lot of data;