The Current empire tree is not quite as usefull. This is for several reasons.

(a) All Herores are displayed, even those sitting in a town and those in the army of another hero. Typically these heroes are not accessed individually.

( Regular troops are not shown

(c) Important information is not accessible (army strength, relation (location) between cities and heroes, and heroes themselves)

(d) city functions should be accessible (as also noted by frogboy in one of the video comments)

(e) Not a bit configurable

The image below displays possible changes to the empire tree.

Armies

Instead of Heroes Armies are shown.

These armies could also have the shield icon to indicate their combat strength. Therefore regular troops wihtin an army, do not have to be represented individually. Heroes within an army, however, should be drawn next to it, to indicate their position on the map (Where did that hero go? - Oh it is in the souvereigns army!). Clicking on the shield icon should open the Units details (for comments on this see https://forums.elementalgame.com/387721).

Additionally displaying regular troops in the empire tree will make it easy to find that one explorer or frigate somewhere on the map. It will also help notice armies that have not moved this turn. Especially transports with heroes onboard are a must-have then.

For caster heroes also a quick button to access spells could be shown on mouseover (similar as described below for cities).

Cities

Cities should display the army strength as well as all heroes stationed within. Here also the shield icon can give access to stationed troops window. A build and recruit button could be shown on mouseover (dynamically move the other icons in the tree to create a clear area for this).

Furthermore each city should have an individual icon. These icons could either be user generated or automatically drawn upon founding of the city.

At a last point cities within the empire tree should be arranged in a definite Order. Preferable by the date when they entered your empire. Having the second oldest city somewhere in the middle of the empire tree is somewhat confusing.

Configuration

To reduce clutter during the later parts of the game the tree should be configurable. Like in Sins you should be able to completely hide armies and cities from the tree (e.g. by right click menues). Furthermore options to hide the champions within armies and army strength should be available.

You could even go further and allow grouping of cities and armies, so, e.g., by continent or user defined attributes. This would allow to hide all cities on one continent and show them again with one click.