I like the empire tree idea and liked it in Sins also. Though the one in elemental seems a bit sparse and lacking the same sense of detail. Right now it seems to only display Heroes and highlighted if they have movement left, as well as Cities and if they are currently building anything. But I think it should display more information.

Here is a list of some of the changes I think it help improve the feedback it gives to the player.

1) Cities don't light up when they have no room for new buildings. This is kinda annoying it lights up thus saying it's ready to build but there is no space in the city.

2) Normal units should appear on the tree. A lot of times you may have a couple scouts around the map and it'd be nice to have the same feedback on them as you do on heroes.

3) Normal units on the tree should be by stack rather then individual unit like heroes. This way if you have a large army in one stack it doesn't fill up the pages on the empire tree.

4) Stacks on the tree should display with the token icons in a row the way they do now so you can see what units are in them. With option to minimize stack so only the top token icon appears with the others placed under it so you can see their is a stack but it's not spread across the screen.

5) Cities have option to expand info which displays unit icons for units garrisoned there.

6) Haven't done/seen sieging yet so don't know if something like this is in. Have city highlight red when it's being sieged.

7) Unit that was attacked during other players turn are highlighted red or some other indication.