Filter tree view by first level only, but still be able to expand

I have a tree

• a
  • x.1
  • x.2
  • x.3
    • y.1.1
    • y.1.2
• b
  • z.1
    • t.1
  • z.2
• c
  • w.1
    • g.1.1
    • g.1.2

I want to have a text box filter at the top of the tree that when you type "b" in, it only shows the first level "b" as a result, but also allows you to expand b to see its children (all of them, not filtered).  The customer is only interested in searching the root level, but is very interested seeing all the children of the filtered root.  Is this possible?

Typing in 'b' in the search would display 

• b

Then Expanding b would display all children of b

• b
  • z.1
    • t.1
  • z.2