What is the fastest way to determine biome? (Unity2D C#)

Question

I've proceduraly generated map and defined biomes based on this scheme:

• Take 3 different maps created via Perlin Noise
• Using presets determine which is the best by matching 3 map values to 3 minimum preset values, example:

Coordinates: [7,8]

A-map = 0.56 
B-map = 0.34
C-map = 0.77 (map values from 0 to 1)

Presets:

Q-preset -> minA = 0.5; minB = 0.3; minC = 0.7
P-preset -> minA = 0.4; minB = 0.2; minC = 0.6
L-preset -> minA = 0.55; minB = 0.33; minC = 0.8

Doing math:

for Q-preset: 0.56-0.5+0.34-0.3+0.77-0.7 = 0.17
for P-preset: 0.56-0.4+0.34-0.2+0.77-0.6 = 0.47
for L-preset: discarded because 0.77 < 0.8 in C-map

The one that is picked is Q-preset, because of the lowest number.

• Choose a random sprite-tile from defined Q-preset to be generated on the map

Here is the problem:

How do I access the information about biome to place different trees on it? For example: I want to randomly pick coordinates to place an object (may be tree), let them be [7,8] Depending on the biome, I want it to be Red if it is Q-preset biome, Green if it is P-preset biome and Yellow if it is L-preset biome. Biome that sits under the [7,8] coordinates is Q-preset biome, but I know this, so how can my program also know this?

What I've thought about this?

• Firstly there could be an index map (Preset biomes are sitting in a list in MapGenerator class, without any pointer/reference to them), similiar to the perlin maps but not 3, just one with index of a biome, but then I don't know how to access this list from MapGenerator in the other class
• Secondly there could be some kind of knowledge, that I didn't google yet - to check what preset does [7,8] tile use, based on that read the name of this preset (ex. "Q-preset"), use this name to generate Tree from preset that is exactly the same ("Q-preset") but not for biome kinds, just tree kinds and pick a tree sprite based on this preset for this certain coordinate pair
• Thirdly I've messed up and there is a much easier way to perform this action

Kindly asking for Your advice, because I'm stuck with this for a few hours and seems like nothing will move without some "click moment" idea or something helpful. I realy don't know how to google it since I'm not very familiar with unity2D, so if You can share some wise words then please do :)