diff --git a/src/constraint_tree.jl b/src/constraint_tree.jl
index 20bd744..d8637d4 100644
--- a/src/constraint_tree.jl
+++ b/src/constraint_tree.jl
@@ -63,7 +63,7 @@ $(TYPEDFIELDS)
 """
 Base.@kwdef struct ConstraintTree
     "Sorted dictionary of elements of the constraint tree."
-    elems::SortedDict{Symbol,Union{Constraint,QConstraint,ConstraintTree}}
+    elems::SortedDict{Symbol,Union{Constraint,QConstraint,ConstraintTree}} = SortedDict()
 
     ConstraintTree(x::SortedDict{Symbol,Union{Constraint,QConstraint,ConstraintTree}}) =
         new(x)
@@ -108,11 +108,15 @@ function Base.getproperty(x::ConstraintTree, sym::Symbol)
     elems(x)[sym]
 end
 
+Base.isempty(x::ConstraintTree) = isempty(elems(x))
+
+Base.length(x::ConstraintTree) = length(elems(x))
+
 Base.keys(x::ConstraintTree) = keys(elems(x))
 
-Base.values(x::ConstraintTree) = values(elems(x))
+Base.haskey(x::ConstraintTree, sym::Symbol) = haskey(elems(x), sym)
 
-Base.length(x::ConstraintTree) = length(elems(x))
+Base.values(x::ConstraintTree) = values(elems(x))
 
 Base.iterate(x::ConstraintTree) = iterate(elems(x))
 Base.iterate(x::ConstraintTree, st) = iterate(elems(x), st)
@@ -121,6 +125,8 @@ Base.eltype(x::ConstraintTree) = eltype(elems(x))
 
 Base.propertynames(x::ConstraintTree) = keys(x)
 
+Base.hasproperty(x::ConstraintTree, sym::Symbol) = haskey(x, sym)
+
 Base.getindex(x::ConstraintTree, sym::Symbol) = getindex(elems(x), sym)
 
 #
diff --git a/src/solution_tree.jl b/src/solution_tree.jl
index 0c1b979..ec348c1 100644
--- a/src/solution_tree.jl
+++ b/src/solution_tree.jl
@@ -26,7 +26,9 @@ SolutionTree(cs, vals)
 $(TYPEDFIELDS)
 """
 Base.@kwdef struct SolutionTree
-    elems::SortedDict{Symbol,Union{Float64,SolutionTree}}
+    elems::SortedDict{Symbol,Union{Float64,SolutionTree}} = SortedDict()
+
+    SolutionTree(x...) = new(x...)
     SolutionTree(x::Constraint, vars::AbstractVector{Float64}) =
         value_product(x.value, vars)
     SolutionTree(x::QConstraint, vars::AbstractVector{Float64}) =
@@ -58,11 +60,15 @@ function Base.getproperty(x::SolutionTree, sym::Symbol)
     elems(x)[sym]
 end
 
+Base.isempty(x::SolutionTree) = isempty(elems(x))
+
+Base.length(x::SolutionTree) = length(elems(x))
+
 Base.keys(x::SolutionTree) = keys(elems(x))
 
-Base.values(x::SolutionTree) = values(elems(x))
+Base.haskey(x::SolutionTree, sym::Symbol) = haskey(elems(x), sym)
 
-Base.length(x::SolutionTree) = length(elems(x))
+Base.values(x::SolutionTree) = values(elems(x))
 
 Base.iterate(x::SolutionTree) = iterate(elems(x))
 Base.iterate(x::SolutionTree, st) = iterate(elems(x), st)
@@ -71,4 +77,6 @@ Base.eltype(x::SolutionTree) = eltype(elems(x))
 
 Base.propertynames(x::SolutionTree) = keys(elems(x))
 
+Base.hasproperty(x::SolutionTree, sym::Symbol) = haskey(x, sym)
+
 Base.getindex(x::SolutionTree, sym::Symbol) = getindex(elems(x), sym)
diff --git a/test/misc.jl b/test/misc.jl
index 7ed7882..3f6de63 100644
--- a/test/misc.jl
+++ b/test/misc.jl
@@ -41,6 +41,13 @@ end
     ct1 = C.variables(keys = [:a, :b])
     ct2 = C.variables(keys = [:c, :d])
 
+    @test isempty(C.ConstraintTree())
+    @test !isempty(ct1)
+    @test haskey(ct1, :a)
+    @test hasproperty(ct1, :a)
+    @test !haskey(ct1, :c)
+    @test !hasproperty(ct1, :c)
+
     @test collect(propertynames(ct1)) == [:a, :b]
     @test [k for (k, _) in ct2] == [:c, :d]
     @test eltype(ct2) == Pair{Symbol,C.ConstraintTreeElem}
@@ -54,6 +61,16 @@ end
     ct = C.variables(keys = [:a, :b])
     @test_throws BoundsError C.SolutionTree(ct, [1.0])
     st = C.SolutionTree(ct, [123.0, 321.0])
+
+    @test isempty(C.SolutionTree())
+    @test isempty(C.SolutionTree(C.ConstraintTree(), Float64[]))
+    @test !isempty(st)
+    @test haskey(st, :a)
+    @test hasproperty(st, :a)
+    @test !haskey(st, :c)
+    @test !hasproperty(st, :c)
+
+    @test length(ct) == length(st)
     @test st.a == 123.0
     @test st[:b] == 321.0
     @test collect(propertynames(st)) == [:a, :b]