How to make a smooth animation transition with a blend tree

Unity Engine
1

So I stumbled into this answer months ago but I forgot it. When I tree to transition from one animation to another on a blendtree, the animator just jumps from one to the other on a dime. I read that Blendtrees are useful because in 3d they can make a smooth transition from one animation to another by blending them together during the transition. What do you have to do so that will happen?

2

gradual change of the variable responsible for this mixing

in BlendTree we can add fields new BlendTree
exampl
BT1 1D from Idle to run , BT2 1D from IdleCrouch to fastCrouch

create BlentTree №3 NO Motion Field but BlendTree field and insert BT1 and 2